<<
Your code has this in it:
Object.prototype.toString.call(this)
which is something you usually do not do. The first argument to the .call
function becomes "this" in the context of the function which is "cheating"
and bypassing prototype inheritance. I consider .call equal to reflection
in Java. You should be doing this.toString().
>>
This is because some primitive types do not support toString
undefined.toString()
VM188:2 Uncaught TypeError: Cannot read property 'toString' of undefined
at <anonymous>:2:10
at Object.InjectedScript._evaluateOn (<anonymous>:895:140)
at Object.InjectedScript._evaluateAndWrap (<anonymous>:828:34)
at Object.InjectedScript.evaluate (<anonymous>:694:21)(anonymous
function) @ VM188:2InjectedScript._evaluateOn @
VM34:895InjectedScript._evaluateAndWrap @ VM34:828InjectedScript.evaluate @
VM34:694
Object.prototype.toString.call(undefined)
"[object Undefined]"
So it becomes a rule of thumb to use Object.prototype.toString rather than
call .toString on the object and sometimes have JS throw an exception
See this:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/toString
On Tue, Sep 8, 2015 at 9:45 AM, Thomas Heller <th.hel...@gmail.com> wrote:
>
> >
> > var x = T
> > x.prototype.whatAmI()
> > prints: {type: "[object Object]", isEqualToPrototype: true} <----
> because 'this' in whatAmI now points to T.prototype
> >
>
> The thing is that you are not supposed to call methods on the prototype
> directly.
>
> Your code has this in it:
>
> Object.prototype.toString.call(this)
>
> which is something you usually do not do. The first argument to the .call
> function becomes "this" in the context of the function which is "cheating"
> and bypassing prototype inheritance. I consider .call equal to reflection
> in Java. You should be doing this.toString().
>
> I cannot explain prototype inheritance well enough and will probably only
> cause more confusion at this point. [1] does a way better job than I ever
> could.
>
> Cheers,
> /thomas
>
> [1]
> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain
>
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