worker: add support for Web Workers#64894

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worker: add support for Web Workers #64894

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a467ea6
test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}
panva Aug 1, 2026
1f3ddd7
test: add opt-in process WPT runner
panva Aug 4, 2026
ded3ce7
worker: add support for Web Workers
avivkeller Aug 1, 2026
bf3e70c
test: enable multi-global WPTs
panva Aug 4, 2026
056b9bf
worker: add wpt tests for Web Workers
avivkeller Aug 1, 2026
1beb0ab
fixup!
avivkeller Aug 15, 2026
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1 change: 1 addition & 0 deletions benchmark/misc/startup-core.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
const warmup = 3;
const state = { n, finished: -warmup };
if (mode === 'worker') {
// eslint-disable-next-line no-global-assign
Worker = require('worker_threads').Worker;
spawnWorker(script, bench, state);
} else {
Expand Down
9 changes: 9 additions & 0 deletions doc/api/cli.md
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Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down
103 changes: 103 additions & 0 deletions doc/api/globals.md
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Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
console.log(event.data); // Prints: Hello from greeter!
worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
`blob:` URLs. Any other scheme makes `new Worker()` throw a
`NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
MIME types are validated only for `data:` and `blob:` URLs. The
`credentials` option is validated for API compatibility but has no effect,
since no network request is made.
* On the main thread, relative script URLs are resolved against the current
working directory, because there is no document base URL. Within a worker
they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.

Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
specification's "closing flag" algorithm, so code remaining in the current
task after `close()` is not executed.
* The worker global is the normal Node.js global object with
`DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
a fresh global created from the interface. Node.js globals such as
`process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
`error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
`0`. An uncaught exception terminates the worker thread, and an unhandled
`error` event is not propagated further: it neither reaches the parent's
global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
their handler properties exist: `languagechange`, `online`, and `offline`,
since these concepts do not exist in Node.js; `rejectionhandled` and
`unhandledrejection`, since Node.js exposes the equivalent does not
implement the `PromiseRejectionEvent` interface or the per-rejection
`preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down
5 changes: 5 additions & 0 deletions doc/node.1
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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down
1 change: 1 addition & 0 deletions eslint.config.mjs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
WritableStreamDefaultWriter: 'readonly',
WritableStreamDefaultController: 'readonly',
WebSocket: 'readonly',
Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.
},
},
},
Expand Down
4 changes: 4 additions & 0 deletions lib/eslint.config_partial.mjs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
name: 'WebAssembly',
message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
},
{
name: 'Worker',
message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
},
{
name: 'WritableStream',
message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down
44 changes: 41 additions & 3 deletions lib/internal/blob.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
if (!isBlob(this))
return PromiseReject(new ERR_INVALID_THIS('Blob'));

dec ??= new TextDecoder();
const dec = getUtf8Decoder();

return PromisePrototypeThen(
arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
return promise;
}

/**
* Read a blob's data synchronously. This is only possible when every part
* of the blob is memory-resident, in which case the reader's pull callbacks
* are invoked synchronously; otherwise (e.g. for file-backed blobs)
* undefined is returned.
* @param {Blob} blob
* @returns {ArrayBuffer|undefined}
*/
function getBlobDataSync(blob) {
const reader = blob[kHandle].getReader();
const buffers = [];
let result;
let ended = false;
while (!ended) {
let sync = false;
reader.pull((status, buffer) => {
sync = true;
if (status === 0) {
// EOS; buffer should be undefined here.
result = concat(buffers);
ended = true;
return;
} else if (status < 0) {
ended = true;
return;
}
if (buffer !== undefined)
ArrayPrototypePush(buffers, buffer);
});
if (!sync) {
// The data is not available synchronously.
break;
}
}
return result;
}

function createBlobReaderStream(reader) {
return new lazyReadableStream({
type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
createBlobFromFilePath,
createBlobReaderIterable,
createBlobReaderStream,
getBlobDataSync,
isBlob,
kHandle,
kType,
resolveObjectURL,
TransferableBlob,
};
2 changes: 2 additions & 0 deletions lib/internal/bootstrap/web/exposed-window-or-worker.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.
// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down
9 changes: 9 additions & 0 deletions lib/internal/encoding.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
},
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
utf8Decoder ??= new TextDecoder();
return utf8Decoder;
}

module.exports = {
getEncodingFromLabel,
getUtf8Decoder,
TextDecoder,
TextEncoder,
};
12 changes: 11 additions & 1 deletion lib/internal/event_target.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
return;

type = webidl.converters.DOMString(type);
const capture = options?.capture === true;
// Flatten the options argument like addEventListener does.
// Refs: https://dom.spec.whatwg.org/#concept-flatten-options
const capture = typeof options === 'boolean' ?
options : options?.capture === true;

if (this[kEvents] === undefined)
return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

function set(value) {
validateThisInternalField(this, kHandlers, 'EventTarget');
// Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
// that are neither callable nor objects deactivate the handler.
// Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
if (typeof value !== 'function' &&
(typeof value !== 'object' || value === null)) {
value = null;
}
if (this[kHandlers] === undefined)
this[kHandlers] = new SafeMap();
let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading
, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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worker: add support for Web Workers#64894

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worker: add support for Web Workers
#64894
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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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avivkeller
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worker: add support for Web Workers
#64894
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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
worker: add support for Web Workers#64894

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 Closed

avivkeller
wants to merge
6
commits into

from

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worker: add support for Web Workers
#64894
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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

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Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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worker: add support for Web Workers
#64894
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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
worker: add support for Web Workers#64894

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 Closed

avivkeller
wants to merge
6
commits into

from

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worker: add support for Web Workers
#64894
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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
Comment thread
avivkeller marked this conversation as resolved.

// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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a467ea6

test: accomodate multi-global tests in WPT{Runner,TestSpec,Report}


panva Aug 1, 2026
1f3ddd7

test: add opt-in process WPT runner


panva Aug 4, 2026
ded3ce7

worker: add support for Web Workers


avivkeller Aug 1, 2026
bf3e70c

test: enable multi-global WPTs


panva Aug 4, 2026
056b9bf

worker: add wpt tests for Web Workers


avivkeller Aug 1, 2026
1beb0ab

fixup!


avivkeller Aug 15, 2026

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1 change: 1 addition & 0 deletions
benchmark/misc/startup-core.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -64,6 +64,7 @@ function main({ n, script, mode }) {
 const warmup = 3;
 const state = { n, finished: -warmup };
 if (mode === 'worker') {
 // eslint-disable-next-line no-global-assign
 Worker = require('worker_threads').Worker;
 spawnWorker(script, bench, state);
 } else {
Expand Down

9 changes: 9 additions & 0 deletions
doc/api/cli.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1563,6 +1563,14 @@ changes:

Enable experimental WebAssembly System Interface (WASI) support.

### `--experimental-web-worker`

<!-- YAML
added: REPLACEME
-->

Enable experimental support for the Web Worker API.

### `--experimental-worker-inspection`

<!-- YAML
Expand DownExpand Up@@ -3889,6 +3897,7 @@ one is included in the list below.
* `--experimental-vfs`
* `--experimental-vm-modules`
* `--experimental-wasi-unstable-preview1`
* `--experimental-web-worker`
* `--force-context-aware`
* `--force-fips`
* `--force-node-api-uncaught-exceptions-policy`
Expand Down

103 changes: 103 additions & 0 deletions
doc/api/globals.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1310,6 +1310,105 @@ changes:
A browser-compatible implementation of {WebSocket}. Disable this API
with the [`--no-experimental-websocket`][] CLI flag.

## Class: `Worker`

<!-- YAML
added: REPLACEME
-->

> Stability: 1 - Experimental. Enable this API with the
> [`--experimental-web-worker`][] CLI flag.

A mostly browser-compatible implementation of Web Workers of the [HTML Standard][],
implemented on top of [`node:worker_threads`][]. Threads created with it
are given the {DedicatedWorkerGlobalScope} API (`self`,
`name`, `location`, `navigator`, `postMessage()`, `close()`, and
`importScripts()`), in addition to the usual Node.js globals, such as `process`.

```js
// worker.js
addEventListener('message', (event) => {
 postMessage(`${event.data} from ${name}!`);
});
```

```js
// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
 console.log(event.data); // Prints: Hello from greeter!
 worker.terminate();
});

worker.postMessage('Hello');
```

Because their lifetime and sharing model depend on origins and
browsing contexts, Node.js does not currently implement `SharedWorker`.

### Loading worker scripts

Worker scripts are read synchronously from the local file system or from
memory rather than fetched over the network, which changes which URLs are
accepted and how failures are reported:

* `new Worker()` and `importScripts()` accept only `file:`, `data:`, and
 `blob:` URLs. Any other scheme makes `new Worker()` throw a
 `NotSupportedError` and `importScripts()` throw a `NetworkError`.
* A script that cannot be read makes `importScripts()` throw a `NetworkError`;
 for `new Worker()` it fires an `error` event at the `Worker` object.
* Redirects, the `nosniff` check, and HTTP MIME type validation do not apply.
 MIME types are validated only for `data:` and `blob:` URLs. The
 `credentials` option is validated for API compatibility but has no effect,
 since no network request is made.
* On the main thread, relative script URLs are resolved against the current
 working directory, because there is no document base URL. Within a worker
 they are resolved against the worker's own URL (as is done in the spec).
* For `blob:` URLs, the script must be held in memory, so blobs backed by a file,
 such as those returned by [`fs.openAsBlob()`][], cannot be used.

### Differences from the HTML Standard
Comment thread
avivkeller marked this conversation as resolved.


Besides script loading, mentioned above:

* Node.js has no origin model, so same-origin and cross-origin distinctions do
 not exist and `location.origin` is `'null'` for every supported scheme.
* `close()` terminates the worker immediately instead of following the
 specification's "closing flag" algorithm, so code remaining in the current
 task after `close()` is not executed.
* The worker global is the normal Node.js global object with
 `DedicatedWorkerGlobalScope` inserted into its prototype chain, rather than
 a fresh global created from the interface. Node.js globals such as
 `process`, `Buffer`, and `require()` remain available to worker scripts.
* `ErrorEvent`s dispatched at `Worker` instances include `message` and
 `error`, but `filename`, `lineno`, and `colno` are always `''`, `0`, and
 `0`. An uncaught exception terminates the worker thread, and an unhandled
 `error` event is not propagated further: it neither reaches the parent's
 global scope nor affects the exit code of the process.
* The following {WorkerGlobalScope} events are never dispatched, although
 their handler properties exist: `languagechange`, `online`, and `offline`,
 since these concepts do not exist in Node.js; `rejectionhandled` and
 `unhandledrejection`, since Node.js exposes the equivalent does not
 implement the `PromiseRejectionEvent` interface or the per-rejection
 `preventDefault()` behavior required by the HTML Standard.

### Web Workers and `node:worker_threads`

Every Web Worker is backed by a [`node:worker_threads`][] {Worker}, so the
two APIs share their threading, structured clone, and transfer semantics.
Inside a worker, \[`worker_threads.parentPort`]\[] is the port behind
`self.postMessage()` and the worker's `message` events, `isMainThread` is
`false`, and `workerData` is `undefined`.

As a rule of thumb, use [`node:worker_threads`][] directly when a program
needs `workerData`, a custom `env` or `execArgv`, resource limits, stdio
redirection, the `'online'` and `'exit'` events, or `worker.threadId`;
`Worker` accepts only the `name`, `type`, and `credentials` options and,
per the specification, its `terminate()` returns `undefined`, rather than
a promise. Threads started through [`node:worker_threads`][] are ordinary
Node.js threads and do not get the worker global scope APIs.

## Class: `WritableStream`

<!-- YAML
Expand DownExpand Up@@ -1355,10 +1454,12 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[CommonJS module]: modules.md
[CommonJS modules]: modules.md
[ECMAScript module]: esm.md
[HTML Standard]: https://html.spec.whatwg.org/multipage/workers.html
[Navigator API]: https://html.spec.whatwg.org/multipage/system-state.html#the-navigator-object
[RFC 5646]: https://www.rfc-editor.org/rfc/rfc5646.txt
[Web Crypto API]: webcrypto.md
[`--experimental-eventsource`]: cli.md#--experimental-eventsource
[`--experimental-web-worker`]: cli.md#--experimental-web-worker
[`--localstorage-file`]: cli.md#--localstorage-filefile
[`--no-experimental-global-navigator`]: cli.md#--no-experimental-global-navigator
[`--no-experimental-websocket`]: cli.md#--no-experimental-websocket
Expand DownExpand Up@@ -1410,9 +1511,11 @@ A browser-compatible implementation of [`WritableStreamDefaultWriter`][].
[`console`]: console.md
[`exports`]: modules.md#exports
[`fetch()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
[`fs.openAsBlob()`]: fs.md#fsopenasblobpath-options
[`globalThis`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis
[`localStorage`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage
[`module`]: modules.md#module
[`node:worker_threads`]: worker_threads.md
[`perf_hooks.performance`]: perf_hooks.md#perf_hooksperformance
[`process.nextTick()`]: process.md#processnexttickcallback-args
[`process` object]: process.md#process
Expand Down

5 changes: 5 additions & 0 deletions
doc/node.1

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Original file line numberDiff line numberDiff line change
Expand Up@@ -836,6 +836,9 @@ Enable experimental ES Module support in the \fBnode:vm\fR module.
.It Fl -experimental-wasi-unstable-preview1
Enable experimental WebAssembly System Interface (WASI) support.
.
.It Fl -experimental-web-worker
Enable experimental support for the Web Worker API.
.
.It Fl -experimental-worker-inspection
Enable experimental support for the worker inspection with Chrome DevTools.
.
Expand DownExpand Up@@ -2022,6 +2025,8 @@ one is included in the list below.
.It
\fB--experimental-wasi-unstable-preview1\fR
.It
\fB--experimental-web-worker\fR
.It
\fB--force-context-aware\fR
.It
\fB--force-fips\fR
Expand Down

1 change: 1 addition & 0 deletions
eslint.config.mjs

View file


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Original file line numberDiff line numberDiff line change
Expand Up@@ -151,6 +151,7 @@ export default [
 WritableStreamDefaultWriter: 'readonly',
 WritableStreamDefaultController: 'readonly',
 WebSocket: 'readonly',
 Worker: 'readonly',
Comment thread
avivkeller marked this conversation as resolved.

 },
 },
 },
Expand Down

4 changes: 4 additions & 0 deletions
lib/eslint.config_partial.mjs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -296,6 +296,10 @@ export default [
 name: 'WebAssembly',
 message: 'Use `const { WebAssembly } = globalThis;` instead of the global.',
 },
 {
 name: 'Worker',
 message: "Use `const { Worker } = require('internal/webworker');` instead of the global.",
 },
 {
 name: 'WritableStream',
 message: "Use `const { WritableStream } = require('internal/webstreams/writablestream')` instead of the global.",
Expand Down

44 changes: 41 additions & 3 deletions
lib/internal/blob.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -30,7 +30,7 @@ const {
} = internalBinding('buffer');

const {
TextDecoder,
getUtf8Decoder,
 TextEncoder,
} = require('internal/encoding');
const { URL } = require('internal/url');
Expand DownExpand Up@@ -88,7 +88,6 @@ let ReadableStream;
let TextDecoderStream;

const enc = new TextEncoder();
let dec;

// Yes, lazy loading is annoying but because of circular
// references between the url, internal/blob, and buffer
Expand DownExpand Up@@ -312,7 +311,7 @@ class Blob {
 if (!isBlob(this))
 return PromiseReject(new ERR_INVALID_THIS('Blob'));

 dec ??= new TextDecoder();
const dec = getUtf8Decoder();

 return PromisePrototypeThen(
 arrayBuffer(this),
Expand DownExpand Up@@ -466,6 +465,43 @@ function arrayBuffer(blob) {
 return promise;
}

/**
 * Read a blob's data synchronously. This is only possible when every part
 * of the blob is memory-resident, in which case the reader's pull callbacks
 * are invoked synchronously; otherwise (e.g. for file-backed blobs)
 * undefined is returned.
 * @param {Blob} blob
 * @returns {ArrayBuffer|undefined}
 */
function getBlobDataSync(blob) {
 const reader = blob[kHandle].getReader();
 const buffers = [];
 let result;
 let ended = false;
 while (!ended) {
 let sync = false;
 reader.pull((status, buffer) => {
 sync = true;
 if (status === 0) {
 // EOS; buffer should be undefined here.
 result = concat(buffers);
 ended = true;
 return;
 } else if (status < 0) {
 ended = true;
 return;
 }
 if (buffer !== undefined)
 ArrayPrototypePush(buffers, buffer);
 });
 if (!sync) {
 // The data is not available synchronously.
 break;
 }
 }
 return result;
}

function createBlobReaderStream(reader) {
 return new lazyReadableStream({
 type: 'bytes',
Expand DownExpand Up@@ -644,8 +680,10 @@ module.exports = {
 createBlobFromFilePath,
 createBlobReaderIterable,
 createBlobReaderStream,
 getBlobDataSync,
 isBlob,
 kHandle,
 kType,
 resolveObjectURL,
 TransferableBlob,
};

2 changes: 2 additions & 0 deletions
lib/internal/bootstrap/web/exposed-window-or-worker.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -51,6 +51,8 @@ exposeLazyInterfaces(globalThis, 'internal/worker/io', ['BroadcastChannel']);
exposeLazyInterfaces(globalThis, 'internal/worker/io', [
 'MessageChannel', 'MessagePort',
]);
// https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
exposeLazyInterfaces(globalThis, 'internal/webworker', ['Worker']);
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// https://www.w3.org/TR/FileAPI/#dfn-Blob
exposeLazyInterfaces(globalThis, 'internal/blob', ['Blob']);
// https://www.w3.org/TR/FileAPI/#dfn-file
Expand Down

9 changes: 9 additions & 0 deletions
lib/internal/encoding.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -614,8 +614,17 @@ ObjectDefineProperties(TextDecoder.prototype, {
 },
});

// A lazily created TextDecoder for the common case of decoding UTF-8 with
// the default options, shared between internal modules.
let utf8Decoder;
function getUtf8Decoder() {
 utf8Decoder ??= new TextDecoder();
 return utf8Decoder;
}

module.exports = {
 getEncodingFromLabel,
 getUtf8Decoder,
 TextDecoder,
 TextEncoder,
};

12 changes: 11 additions & 1 deletion
lib/internal/event_target.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -722,7 +722,10 @@ class EventTarget {
 return;

 type = webidl.converters.DOMString(type);
 const capture = options?.capture === true;
 // Flatten the options argument like addEventListener does.
 // Refs: https://dom.spec.whatwg.org/#concept-flatten-options
 const capture = typeof options === 'boolean' ?
 options : options?.capture === true;

 if (this[kEvents] === undefined)
 return;
Expand DownExpand Up@@ -1163,6 +1166,13 @@ function defineEventHandler(emitter, name, event = name) {

 function set(value) {
 validateThisInternalField(this, kHandlers, 'EventTarget');
 // Event handler IDL attributes are [LegacyTreatNonObjectAsNull]: values
 // that are neither callable nor objects deactivate the handler.
 // Refs: https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-idl-attributes
 if (typeof value !== 'function' &&
 (typeof value !== 'object' || value === null)) {
 value = null;
 }
 if (this[kHandlers] === undefined)
 this[kHandlers] = new SafeMap();
 let wrappedHandler = this[kHandlers].get(event);
Expand Down
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