What is the "this" pointer for global functions?

Question

Possible Duplicates:
'this' keyword, not clear
this operator in javascript

function foo()
{
    if(this === window)
        return null;

    return 1;
}

var i = foo(); // returns 1;

What is the this member of a global function, and how can I test from within a function if it's being called in a global scope or as a member function?

Edit: It seems JQuery makes a difference here, since everybody assures me foo should return null for run-of-the-mill JavaScript. How does JQuery change this?

Note that the OP says, in a comment, below, that this is in a Greasemonkey script.

Also, http://stackoverflow.com/questions/3127429/javascript-this-keyword and http://stackoverflow.com/questions/3320677/this-operator-in-javascript/ — StriplingWarrior, Jul 07 '11 at 18:27

Gabriele Petrioli · Answer 1 · 2011-07-07T18:36:00.840

3

this refers to the window object in this case.

Just do alert(this); and it will say [object Window]

But if you do

var i = new foo(); // returns an object (instance of foo);

then this refers to the instance of foo.

edited Jul 07 '11 at 18:36

answered Jul 07 '11 at 18:24

Gabriele Petrioli

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So could you say `if (this == window) ...`? – mellamokb Jul 07 '11 at 18:25
`if (this === window)` will work .. but it will always be true for those.. – Gabriele Petrioli Jul 07 '11 at 18:26
I've tried this (in Firefox 4), and I get the error "Could not convert JavaScript argument arg 2 [nsIPromptService.alert]" – bfops Jul 07 '11 at 18:28
@robot, Is this for firefox plugin ? – Gabriele Petrioli Jul 07 '11 at 18:34
`this` refers to the global object, which may *or may not* be `window`, depending on the environment. – Andy E Jul 07 '11 at 18:43

score 3 · Accepted Answer · answered Jul 07 '11 at 18:56

According to this the difference is because of greasemonkey (not JQuery).

A Greasemonkey user script, however, by default wraps up all code inside an anonymous function wrapper that swallows identifiers, causing them not to end up on the global object.

It goes on to say that you can use @unwrap to make this point to the window as it does with regular on-page Javascript.

score 0 · Answer 3 · answered Jul 07 '11 at 18:28

0

The this member refers to the entire page, and will always be defined - your foo() method will never return null.

answered Jul 07 '11 at 18:28

MuffinMan

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score -1 · Answer 4 · edited Jul 07 '11 at 18:27

-1

this always points on the current element. In the case of foo(), this points to window.

edited Jul 07 '11 at 18:27

Lightness Races in Orbit

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answered Jul 07 '11 at 18:25

aruss

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(I've edited your answer to make it clearer. "This" and "window" are words in English, as well as important terms in Javascript.) – Lightness Races in Orbit Jul 07 '11 at 18:27
Testing `this == foo` returns false. – bfops Jul 07 '11 at 18:29
Oops; testing `this == window` returns false. – bfops Jul 07 '11 at 18:38

What is the "this" pointer for global functions?

4 Answers4