On Oct 14, 4:45 pm, Andy E <andyearns...@gmail.com> wrote:
> I recently discovered that several compatibility implementations of
> Object.keys() on the web will throw an error for DOM objects in
> Internet Explorer 8 and lower.  This differs from the current browsers
> having a native implementation and how the ECMAScript 5th edition
> defines the behaviour of Object.keys.
> The problem lies with the hasOwnProperty() check, which is not a valid
> method on Internet Explorer DOM objects because they aren't instances
> of Object.  The fix is very simple; "borrow"  hasOwnProperty() from
> Object.prototype.hasOwnProperty() instead.  The fixed PrototypeJS
> implementation would be:
>   function keys(object) {
>     if (Type(object) !== OBJECT_TYPE) { throw new TypeError(); }
>     var results = [];
>     for (var property in object) {
>       if (object.prototype.hasOwnProperty.call(object, property)) {
>         results.push(property);
>       }
>     }
>     return results;
>   }

No need to access `hasOwnProperty` off of `Object.prototype` on _every
iteration_, making things unnecessary slow. It's easy enough to alias
`hasOwnProperty` (if it isn't already, somewhere there in the source).

As a side note, this implementation (as well Prototype's original one)
doesn't take care of JScript's DontEnum bug (<IE9, IIRC), which means
`toString`, `valueOf`, etc. -named keys won't be returned. So that's
something else to keep in mind as far as ES5-compatibility goes.


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