The behavior you are seeing is due to javascript auto-boxing the primitive
types. number, string, etc are not objects and have no properties to call. When
the js runtime sees you look up a "property" of a non-object type it boxes the
value with the appropriate object (Number for number, String for string, etc)
before doing protocol lookup. The "this" value you are seeing is the box, which
is why its typeof is object.
You can retrieve the unboxed value from the box using this.valueOf()
On Tuesday, December 17, 2013 7:57:12 AM UTC-6, Chas Emerick wrote:
> As much as I distrust goog.typeOf, this isn't its fault. It's really
>
> quite bizarre: AFAICT, typeof (i.e. the JavaScript operator, not the
>
> goog.typeOf function) returns "object" for any value named by `this`:
>
>
>
> > typeof 5
>
> "number"
>
> > Number.prototype.foo = function () { return typeof this; };
>
> [object Function]
>
> > (5).foo()
>
> "object"
>
>
>
> This is a whole new level of JavaScript wat for me. I've asked the SO
>
> hordes for insight:
>
> http://stackoverflow.com/questions/20636028/typeof-returns-object-for-this-number-elsewhere
>
>
>
> Meanwhile, I've discovered that extending the protocol to both `number`
>
> and `js/Number` does work under both execution contexts, a much more
>
> palatable workaround. That's allowed me to move forward with my
>
> current work.
>
>
>
> Thanks,
>
>
>
> - Chas
>
>
>
> On Tue 17 Dec 2013 04:37:56 AM EST, Thomas Heller wrote:
>
> > FWIW I had some troubles with native types before, mine were related to IE
> > though. The culprit for your troubles is goog.typeOf (which is a basic
> > wrapper arrount js/typeof).
>
> >
>
> > If you run this via phantomjs
>
> >
>
> > -----
>
> > console.log("typeof", typeof(5));
>
> >
>
> > Number.prototype.foo = function() {
>
> > console.log("typeof prototype", typeof(this));
>
> > };
>
> >
>
> > (5).foo();
>
> >
>
> > phantom.exit(0);
>
> > -----
>
> >
>
> > You get
>
> >
>
> > typeof number
>
> > typeof prototype object
>
> >
>
> > Pretty sure the problem goes away cause in advanced compilation cause it
> > gets inlined and (.foo 5) is turned into (m 5) skipping the step with this.
> > Just a guess though.
>
> >
>
> > HTH,
>
> > /thomas
>
> >
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