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a53542e0a3
It's not what the spec tells us to do. In fact, the spec tells us the
exact opposite:
9.5 Jobs and Host Operations to Enqueue Jobs
https://tc39.es/ecma262/#sec-jobs
A Job is an Abstract Closure with no parameters that initiates an
ECMAScript computation when no other ECMAScript computation is
currently in progress.
...
Their implementations must conform to the following requirements:
- ...
- The Abstract Closure must return a normal completion, implementing
its own handling of errors.
However, this turned out to not be true in all cases. More specifically,
the NewPromiseReactionJob AO returns the completion result of calling a
user-provided function (PromiseCapability's [[Resolve]] / [[Reject]]),
which may be an abrupt completion:
27.2.2.1 NewPromiseReactionJob ( reaction, argument )
https://tc39.es/ecma262/#sec-newpromisereactionjob
1. Let job be a new Job Abstract Closure with no parameters that
captures reaction and argument and performs the following steps
when called:
...
h. If handlerResult is an abrupt completion, then
i. Let status be Call(promiseCapability.[[Reject]],
undefined, « handlerResult.[[Value]] »).
i. Else,
i. Let status be Call(promiseCapability.[[Resolve]],
undefined, « handlerResult.[[Value]] »).
j. Return Completion(status).
Interestingly, this case is explicitly handled in the HTML spec's
implementation of jobs as microtasks:
8.1.5.3.3 HostEnqueuePromiseJob(job, realm)
https://html.spec.whatwg.org/webappapis.html#hostenqueuepromisejob
2. Queue a microtask on the surrounding agent's event loop to
perform the following steps:
...
5. If result is an abrupt completion, then report the exception
given by result.[[Value]].
This is precisely what all the major engines do - but not only in
browsers; the provided code snippet in the test added in this commit
works just fine in Node.js, for example.
SpiderMonkey:
https://searchfox.org/mozilla-central/rev/25997ce8267ec9e3ea4b727e0973bd9ef02bba79/js/src/builtin/Promise.cpp#6292
https://searchfox.org/mozilla-central/rev/25997ce8267ec9e3ea4b727e0973bd9ef02bba79/js/src/builtin/Promise.cpp#1277
https://searchfox.org/mozilla-central/rev/25997ce8267ec9e3ea4b727e0973bd9ef02bba79/js/src/vm/JSContext.cpp#845
JavaScriptCore:
https://trac.webkit.org/browser/webkit/trunk/Source/JavaScriptCore/builtins/PromiseOperations.js?rev=273718#L562
https://trac.webkit.org/browser/webkit/trunk/Source/JavaScriptCore/runtime/JSMicrotask.cpp?rev=273718#L94
V8:
https://source.chromium.org/chromium/chromium/src/+/main:v8/src/builtins/promise-abstract-operations.tq;l=481;drc=a760f03a6e99bf4863d8d21c5f7896a74a0a39ea
https://source.chromium.org/chromium/chromium/src/+/main:v8/src/builtins/builtins-microtask-queue-gen.cc;l=331;drc=65c9257f1777731d6d0669598f6fe6fe65fa61d3
This should probably be fixed in the ECMAScript spec to relax the rule
that Jobs may not return an abrupt completion, just like in the HTML
spec. The important bit is that those are not surfaced to user code in
any way.
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| Array | ||
| ArrayBuffer | ||
| Atomics | ||
| BigInt | ||
| Boolean | ||
| DataView | ||
| Date | ||
| Error | ||
| FinalizationRegistry | ||
| Function | ||
| functions | ||
| Infinity | ||
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| JSON | ||
| Map | ||
| Math | ||
| NaN | ||
| Number | ||
| Object | ||
| Promise | ||
| Proxy | ||
| Reflect | ||
| RegExp | ||
| Set | ||
| ShadowRealm | ||
| String | ||
| Symbol | ||
| Temporal | ||
| TypedArray | ||
| WeakMap | ||
| WeakRef | ||
| WeakSet | ||