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fix(replay): Set text/javascript MIME type on compression worker Blob - #22377
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The compression worker is created from a Blob URL, but the Blob was constructed without a MIME type, so it defaulted to an empty type. Safari (especially on iOS) validates the MIME type before executing a Blob as a classic Worker and silently rejects a non-JS type, firing a bare `error` event with no message — surfaced by the SDK as "Failed to load Replay compression worker: Unknown error". Blink/Gecko are lenient here, so this only manifests on Safari. Tagging the Blob `text/javascript` lets the worker load across browsers.
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tbh I can't find a URL that says safari is more prone to not load a worker blob if it doesn't have a MIME type, but seems reasonable to add one.
Slop
getWorkerURL()builds the Replay compression worker from aBlobURL, but theBlobwas created without a MIME type, so it defaulted to an empty type. Safari (especially on iOS) validates the MIME type before executing aBlobas a classicWorkerand silently rejects a non-JS type — firing a bareerrorevent with no message, which the SDK surfaces as:Blink/Gecko are lenient about the blob MIME type, so this particular failure mode is Safari-specific. Tagging the blob
text/javascriptis the standard cross-browser fix.This is a handled error — recording already falls back to the uncompressed buffer — so there is no user-facing behavior change beyond the worker actually loading on Safari.
Testing
packages/replay-worker/test/unit/getWorkerURL.test.tsasserts the blob is created with thetext/javascriptMIME type.oxlint+oxfmtclean;replay-workersuite passes.Notes
This is the low-risk half of a split. A separate follow-up PR handles the cross-browser (Chrome/Edge/Firefox) occurrences of the same captured error, which come from the worker fetch being aborted during page navigation/teardown rather than from the MIME type. Follow-up to #19008, which introduced the descriptive error message but did not address the load failure itself.