592274 - Implementation status table claims we don't support "use strict"

Status: RESOLVED DUPLICATE of bug 482298

(Core :: JavaScript Engine, defect)

Description

[Jonathan Watt [:jwatt]]

The following webpage claims FF4 beta 5 pre doesn't support "use strict":

http://kangax.github.com/es5-compat-table/

See comment at the bottom of the page for how they test.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Looks like a dup of bug 514570?

Comment 2

[Brendan Eich [:brendan]]

It's really just the bug with alias es5strict -- we aren't done yet, but we will be for Mozilla 2.0 / Firefox 4.

/be

Comment 3

[Brendan Eich [:brendan]]

IOW, that |this| coercion bug is supposed to be the very last bug that anyone implementing ES5 strict on top of an ES5-without-strict implementation should fix, lest that (function () { "use strict"; return !this; })() detection technique give the wrong answer.

/be

Comment 4

[Juriy "kangax" Zaytsev]

It's hard to choose one item from the extensive list of things that strict mode brings to the table. The reason I ended up with this-coercion is because, as Brendan says, it's likely one of the last things to be implemented, making it a better indication of "strict mode support". IIRC, `(function(){"use strict"; return !this})()` was also mentioned by Mark Miller on es-discuss some time ago (as, probably, the "shortest" way to test strict mode support), so that little snippet just "sticked". For a more or less complete list of supported features, the link in that same compat table references this page — http://kangax.github.com/es5-compat-table/strict-mode/ , where Mozilla is, in fact, leading right now.

Another option — which I might implement in the future, if I find time — is to perform all of the "strict mode" tests and write percentage, rather than somewhat unfair yes/no.