`ts` object has no properties when loading typescript.js in a browser with v5.5-rc

[lauraharker]

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This came up after sending the initial Google v5.5-beta feedback in #58685 since I was just looking at build failures for that feedback.

Apologies if this isn't an officially supported way of using the TypeScript compiler or not - most of the docs I can find are specific to running the compiler via Node.

Google has some internal web apps that load the bundled TSC from https://github.com/microsoft/TypeScript/blob/v5.5-rc/lib/typescript.js file in a browser. One example use case is a tool similar to https://www.typescriptlang.org/play/.

In TS 5.5 these apps break at runtime because they call methods on the global ts object like ts.createLanguageService, but ts is now just an empty object with no properties. I narrowed this down to the bundling changes in #57133. Here's typescript.js before & after:

v5.4.2:

var ts = (() => {
 // lots and lots of code
 return require_typescript();
})();

if (typeof module !== "undefined" && module.exports) { module.exports = ts; }

v5.5-rc:

var ts = {}; ((module) => {
// lots and lots of code
module.exports = __toCommonJS(typescript_exports);
// even more code
})(typeof module !== "undefined" && module.exports ? module : { exports: ts });
if (typeof module !== "undefined" && module.exports) { ts = module.exports; }

I'd assume that in v5.5-rc, ts was intended to be instantiated via passing {exports : ts } as the module argument to this IIFE, causing the exported functions that are put on module.exports to also be defined as properties on ts. Instead the module.exports = __toCommonJS(typescript_exports); assignment just overwrites ts in {exports: ts} and ts is just an empty object.

[jakebailey]

Ugh, I thought this was tested.

Apparently our browser test only tests that the code executes, not that it actually declares a working global. Will fix this ASAP.

[jakebailey]

Note that I wouldn't 100% consider this supported; it's possible that this loading method may go away in a PR like #58419. But, there's not one form that works for both without going through a bundler or esm.sh or something.

[lauraharker]

Thanks for the quick fix & additional context Jake Bailey (@jakebailey)! We can certainly switch to loading tsc as an ES module in browsers if/when that lands

[fatcerberus]

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