nhiorki@
Can you handle this issue?

Is this related to Issue 590219?

Doesn't seem likely: that issue is about the error event seen _outside_ the worker, while this one is for the error event _inside_ the worker.

Issue 706037 has been merged into this issue.

This is biting people using service workers also.

I'd be interested in seeing if there are WPT tests for this.

Mozilla added a WPT for this in the linked bug: 
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/external/wpt/workers/Worker_ErrorEvent_error.htm

Considering Mozilla vetted the spec and added this test, looks like we just need to get this test passing.

I'm now investigating...

bashi@ helped me to investigate this (thank you!) and we found there're two issues here:

1) In WorkerOrWorkletScriptController.cpp, 'ErrorEvent' is created without 'error' attribute[1]. This results in 'e.error == null' in following code:

  // worker.js
  addEventListener("error", function(e) {
    // e.error == null here because the event is created w/o 'error' attribute.
  });
  throw "hello";

2) Currently, Blink's WorkerGlobalScope.idl does not support "OnErrorEventHandler" interface (see foolip@'s comment on [2]). This results in 'e.error == null' in following code:

  // worker.js
  onerror = function(message, location, line, col, error) {
    // error == null here because the idl does not support this callback signature.
  }
  throw "hello";

I think fixing only the case 1) would be enough for real applications, we need to fix the both cases to pass the web-platform-test (Worker_ErrorEvent_error.htm) though.

[1] https://chromium.googlesource.com/chromium/src/+/f98f8cb0517d4b28943102a007528063252e0ce0/third_party/WebKit/Source/bindings/core/v8/WorkerOrWorkletScriptController.cpp#326
[2] https://chromium.googlesource.com/chromium/src/+/f98f8cb0517d4b28943102a007528063252e0ce0/third_party/WebKit/Source/core/workers/WorkerGlobalScope.idl#38

Agree that fixing 1) is a good first thing to do.

yiyix@, do you think you could take a look at 1) on c#10? Probably, we could...

  1) add a new ctor which takes a ScriptValue and assigns it to |m_error|.
  2) pass |state.exception| to the ctor in [1].
  3) add a new layout test for this change (because the wpt test does not work yet at this point)

^^^ 1) add a new ctor *to ErrorEvent* which takes...

Filed a separate issue for 2) "OnErrorEventHandler" ( issue 708857 )

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0662e1de8c6d9800c4baed479249c1fa5201c24c

commit 0662e1de8c6d9800c4baed479249c1fa5201c24c
Author: yiyix <yiyix@chromium.org>
Date: Thu Apr 06 14:16:37 2017

Update Error Event inside a worker to provide the exact exception value

In WorkerOrWorkletScriptController.cpp, 'ErrorEvent' used to be created
without exception value, so the exception, |m_error|, is always set to
null. A new constructor of ErrorEvent is added in this patch which
takes exception as input and set |m_error| to the exception value.

TEST=error-script.js and error-worker-script.js

BUG= 640724 

Review-Url: https://codereview.chromium.org/2804533002
Cr-Commit-Position: refs/heads/master@{#462458}

[add] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/ServiceWorkerGlobalScope/resources/error-worker.js
[add] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/ServiceWorkerGlobalScope/service-worker-error-event.https.html
[add] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/LayoutTests/fast/workers/dedicated-worker-error-event.html
[add] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/LayoutTests/fast/workers/resources/error-script.js
[modify] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/Source/bindings/core/v8/WorkerOrWorkletScriptController.cpp
[modify] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/Source/core/events/ErrorEvent.cpp
[modify] https://crrev.com/0662e1de8c6d9800c4baed479249c1fa5201c24c/third_party/WebKit/Source/core/events/ErrorEvent.h

Thanks for the fix!