- From: Boris Zbarsky <bzbarsky@MIT.EDU>
- Date: Fri, 08 Nov 2013 13:34:59 -0500
- To: public-script-coord@w3.org
On 11/8/13 1:27 PM, David Bruant wrote:
> Le 07/11/2013 08:31, Garrett Smith a écrit :
>> Also, Array.filter is NaN in Chrome.
> ... I don't even... Whoaaa... isNaN(Array.filter) is true in Firefox as
> well...
>
> When you think you've seen it all...
isNaN is a slightly silly test to use in this case.
In Firefox, Array.filter is a Function object. When you use isNaN, that
invokes ToNumber() on the argument, which per the table at
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-tonumber
invokes ToPrimitive, which lands you at
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-toprimitive and
you get to OrdinaryToPrimitive. This gets the "valueOf" property, which
in this case is Object.prototype.valueOf, which just returns the object
itself. So we keep going, try the "toString" property, which returns a
string like "function filter() {\n [native code]\n}" or whatnot.
Then we call ToNumber() on that string, which of course returns NaN.
And then isNaN returns true.
In Chrome, Array.filter is undefined. The table at
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-tonumber says
to return NaN, and then isNaN returns true.
-Boris
Received on Friday, 8 November 2013 18:35:28 UTC