Intentional breaking change in ES6 draft spec?

Erik Arvidsson erik.arvidsson at
Thu Jun 13 18:59:09 PDT 2013

This was from back in the days when Google code search was still available
and the only hits we found were from test suites.
On Jun 13, 2013 8:54 PM, "Brendan Eich" <brendan at> wrote:

> Luke Hoban wrote:
>> The ES6 draft grammar no longer allows the following, which was legal ES5:
>>      for(var i = 1 in []) {}
>> Was that an intentional breaking change?  If so, why?
> Yes, to simplify and tighten up grammar (and engines). We reckoned that
> only testsuites counted on this. This was recorded in some meeting notes
> but I'm not free to dig them up right now.
>     (Of course, there are exceedingly limited practical uses of this, but
>> that alone doesn't seem to justify a breaking change).
> We had some web crawling help, IIRC. We also figured we had time to test
> and put it back, if needed. Did you find web content using it?
> /be
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