1323615 - unexpected behavior with promise based code inside iterator

Status: RESOLVED DUPLICATE of bug 449811

(Core :: JavaScript Engine, defect)

Description

[djrmuv]

Attachment: t.html

User Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0
Build ID: 20161130084355

Steps to reproduce:

ALSO check the attached file

var arr = ['a', 'b', 'c']

		for (let item of arr) {
			new Promise((resolve, reject) => {
				window.setTimeout(function() {
	                resolve(item);
	            }, Math.random() * 200);
			}).then((v) => {
				console.log(v);
			})
		}


Actual results:

so in chrome it prints a permutation of the arr elements, whereas in firefox it always prints "c" three times. i dont know which should be the correct behavior but the chrome one seems more intuitive

this problem is also present in firefix nightly


Expected results:

logging a permutation of arr

Comment 1

[Tooru Fujisawa [:arai]]

It should be fixed in Firefox 51 (bug 449811)
can you check if it works as expected on Firefox 51 beta?

Comment 2

[djrmuv]

mm yeah it works on the developer edition 51.0a2, but it does not on nightly, but i guess it will also be fixed there thanks.

Comment 3

[Tooru Fujisawa [:arai]]

if it doesn't work on nightly, can you post the standalone testcase?
and also what's the version and build date of the nightly you've tested?

when I evaluate the code in web console, it prints permutation of arr.

Comment 4

[Tooru Fujisawa [:arai]]

I've tested on 53.0a1 (2016-12-13) (64-bit).

Comment 5

[djrmuv]

oh yeah, it work on 53.0a1, sorry.

Comment 6

[Tooru Fujisawa [:arai]]

okay, thank you :)