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

Andrew Paprocki andrew at
Tue Nov 8 17:26:29 PST 2011

On Tue, Nov 8, 2011 at 6:36 PM, Brendan Eich <brendan at> wrote:
> Ignoring performance, a lot of stylish JS hackers use Object.keys(o).forEach. How many run into the wrong |this| (arguments/break/continue/return)? Not clear. Something to study.

I was curious so I did some grok-ing across my code sample and
Object.keys() is barely used. The usage of the |for in| construct is 2
orders of magnitude larger than the usage of hasOwnProperty(),
supporting the thought that no one really does it the "right" way.

The MDN page for Object.keys does not talk about |this| being wrong in
certain situations. If you could elaborate on that, it would be
helpful to know.


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