for own(...) loop (spin-off from Re:, hasOwnProperty(), and inheritance)

Timmy Willison timmywillisn at
Tue Nov 8 13:45:09 PST 2011

Yes, I think JS needs something like this.  This is new to no one here, but
my main concern with using hasOwnProperty is the loss of performance, so I
think it would be worth exploring more than just syntactic sugar.  But I
don't know how realistic it is to hope for that.

On Tue, Nov 8, 2011 at 3:49 PM, Brendan Eich <brendan at> wrote:

> The recommended practice when writing for-in loops in JS today is to write:
>   for (i in o) {
>     if (o.hasOwnProperty(i)) {
>       *body*
>     }
>   }
> Although many JS developers do not follow the recommendation (out of
> ignorance or intentionally, doesn't matter).
> Should provide sugar for the recommended pattern? To make it
> compose with declarations and destructuring in the for head, it should use
> a contextual keyword immediately after 'for':
>   for own (i in o) {
>     *body*
>   }
> This is a small thing but it might pay off in the long run.
> /be
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> es-discuss at
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