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stream: drop rejection step for sync transforms #67339

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stream: drop rejection step for sync transforms #67339

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15 changes: 7 additions & 8 deletions lib/internal/webstreams/transformstream.js
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Original file line number Diff line number Diff line change
Expand Up @@ -592,11 +592,11 @@ function transformStreamDefaultControllerError(controller, error) {

// Mirrors the reference implementation's
// `promiseCall(transformAlgorithm, ...).then(undefined, rejectionSteps)`:
// the returned promise settles one microtask after the (coerced) result
// does, and a rejection errors the transform stream before propagating.
// The raw transform callback plus the shared resolved promise for
// non-thenable results replace the previous async wrapper's two implicit
// promises per chunk.
// a rejection errors the transform stream before propagating. A
// non-thenable result cannot reject, so it maps to the shared resolved
// promise without the rejection step; the write then completes one
// microtask earlier than in the reference implementation, with the
// relative order of all stream events unchanged.
function transformStreamDefaultControllerPerformTransform(controller, chunk) {
const controllerState = controller[kState];
const transformAlgorithm = controllerState.transformAlgorithm;
Expand All @@ -612,10 +612,9 @@ function transformStreamDefaultControllerPerformTransform(controller, chunk) {
}
if (result === null ||
(typeof result !== 'object' && typeof result !== 'function')) {
result = kResolvedPromise;
} else {
result = PromiseResolve(result);
return kResolvedPromise;
}
result = PromiseResolve(result);
controllerState.performTransformRejected ??= (error) => {
transformStreamError(controller[kState].stream, error);
throw error;
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