why is the object "this" not reference to the global window object?

Question

The Foo is being executed from the window global object like this:

  new Foo();   // false why?
  Foo();       // true

 function Foo()
 { 
     alert(this == window); 
 };

But when I run this function Foo code, the alert message says false, why is this when Foo is executed from the global window object?

score 3 · Accepted Answer · answered Sep 21 '18 at 18:32

It's because you used new. The new operator creates a new object, sets that object's prototype to be Foo.prototype, then invokes Foo with this set equal to the newly-created object.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

ControlAltDel · Answer 2 · 2018-09-21T18:34:56.210

1

It's not in the window context. It's in the function context. If you'd like it to be in the window context, you can do

foo.call(window);

edited Sep 21 '18 at 18:34

answered Sep 21 '18 at 18:31

ControlAltDel

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Foo(); // true, new Foo(); // false, what context is it in because "this" is an object.. – Nora Sep 21 '18 at 18:34
1

@Nora sorry it's getting late in the day. I meant to say it *is* in the function context – ControlAltDel Sep 21 '18 at 18:35

score -2 · Answer 3 · edited Sep 21 '18 at 18:38

-2

JavaScript has function-level scoping. In your example, this is referring to the Foo function.

edited Sep 21 '18 at 18:38

Ele

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answered Sep 21 '18 at 18:31

Strikegently

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this == Foo // still says false – Nora Sep 21 '18 at 18:35

why is the object "this" not reference to the global window object?

3 Answers3