Usage shortcuts of arguments object breaks old version of WebKit

[aaronjensen]

Ok, this is an odd one and is more likely a (fixed) webkit issue and not a core-js issue, but I wanted to point it out here in case you wanted to do something about it.

This change: 5bcabca#diff-f68e573b7ecfc93a7afcce675b0459eaL24

Causes this error:

TypeError: 'undefined' is not an object (evaluating '$$[index++]')

On this stack in capybara-webkit:

Linux id16784 3.8.0-44-generic #66~precise1-Ubuntu SMP Tue Jul 15 04:01:04 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
Capybara: 2.5.0
capybara-webkit: 1.7.1
Qt: 5.0.2
WebKit: 537.21
QtWebKit: 5.1.1

But it works fine on OS X with a newer version of Qt:

Capybara: 2.5.0
capybara-webkit: 1.7.1
Qt: 5.5.1
WebKit: 538.1
QtWebKit: 5.5.1

[zloirock]

Interesting. It means this code doesn't work in this WebKit version:

(function(){
  var $$ = arguments;
  return $$[0];
})(42);

Can you confirm it?

[aaronjensen]

That doesn't appear to cause it.

I also tried

(function(){ var $$ = arguments, $$len = $$.length, i = 0; while(i<$$len){ $$[i]; i++; } })(42, 43)

and that didn't cause it either. If I console.log($$) within the while loop or check it with if(!$$) {...} it doesn't repro.

[zloirock]

I have no ideas what else can cause this problem. Can you add some additional info - version, line, stack, etc?

[aaronjensen]

As I mentioned in chat, I can't get much more info. Here is the line causing it:

    const props = {
      ...this.props,
      href: path + wrappedWindow.location.search,
      onClick(e) {
        e.preventDefault()
        navigationActions.changePath(path)
      },
    }

It is in a react component that is rendered several times on a page. It's only the last call to it that has the problem, all the others are fine.

[aaronjensen]

It happens after maybe 80 calls to it, so it's very likely a broken optimization

[aaronjensen]

Great, thanks. Any chance of a 1.2.7 w/ this applied?

[zloirock]

It's not a critical bug (a very specific engine), so I don't think makes sense publish 1.2.7. Today I'll publish 2.0.0-beta.2, stable 2.0 will be available when I will fix some other problems.

[aaronjensen]

Ok, thanks. I don't think I can use 2.0 yet because too many things are pinned to 1.0 but I forked it, so it's ok. Thanks!

[zloirock]

Fixed in 2.0.