On 11/04/2011, at 05:14, Mark S. Miller wrote:
>
> On Apr 10, 2011, at 22:18 , David Herman wrote:
>
> > function getDefiningObject(obj, key) {
> > if (!(key in obj))
> > throw new Error("key " + key + " not found");
> > while (!obj.hasOwnProperty(key))
>
> That should be
>
> while (!{}.hasOwnProperty.call(obj, key))
>
> which works even if obj has an own property named 'hasOwnProperty'.
And also because that would work for null too, unlike (null).hasOwnProperty(
key ) that would throw "TypeError: 'null' is not an object (evaluating
'(null).hasOwnProperty')", and null is at the end of the prototype chain of all
objects...
Here's another take on it:
function getDefiningObject (o, key) {
do {
if ( {}.hasOwnProperty.call(o, key) ) break;
} while ( o = Object.getPrototypeOf(o) );
return o;
}
getDefiningObject([1,2], 'length')
[1, 2]
getDefiningObject([1,2], 'pop')
[]
getDefiningObject([1,2], 'valueOf')
Object
getDefiningObject([1,2], 'none')
null
--
Jorge.
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