1072932 - TDZ buglet in test_eventemitter_basic.html

Status: RESOLVED FIXED

(DevTools :: General, defect)

Description

[Tom Tromey :tromey]

I had a "try" build fail in test_eventemitter_basic.html.
The error says in part:

ReferenceError: can't access let declaration `beenHere1' before initialization: next@chrome://mochitests/content/chrome/toolkit/devtools/tests/mochitest/test_eventemitter_basic.html:61:14
ReferenceError: can't access let declaration `beenHere1' before initialization: next@chrome://mochitests/content/chrome/toolkit/devtools/tests/mochitest/test_eventemitter_basic.html:61:14


Looking at `beenHere1' I see:

      function testEmitter(aObject) {
...
        emitter.on("next", next);
        emitter.emit("next", "abc", "def");

        let beenHere1 = false;
        function next(eventName, str1, str2) {
...

So I think that `beenHere1' is calling into the "temporal dead zone":
depending on the circumstances, `next' may be called before `beenHere1'
has been bound.

The fix is to hoist the `let' up above the call to `emitter.on'.
I'll attach a patch momentarily.

Comment 1

[Tom Tromey :tromey]

Attachment: hoist "let"s to avoid the TDZ

I hoisted "beenHere2" as well since it seemed possible for "onlyOnce"
to be called before that let binding was seen.

I looked at the other files in this directory and everything else was
fine.

Comment 2

[Panos Astithas (he/him) [:past] (please ni?)]

Comment on attachment 8495260 [details] [diff] [review]
hoist "let"s to avoid the TDZ

Review of attachment 8495260 [details] [diff] [review]:
-----------------------------------------------------------------

Nice, I've seen that error recently myself.

Comment 3

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/d056ffd17f0c

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/d056ffd17f0c