What is the reasoning behind declaring var that = this; in javascript?

Question

I came across this many times in a new code base that I'm looking at and was wondering is there is any proper reasoning behind it?

related: http://stackoverflow.com/questions/7234282/what-is-the-reason-for-var-this-this?rq=1 — Niko, May 28 '13 at 14:26
Take the code, and try to substitute `this` for `that` where used, and you'll see that it likely won't work. — , May 28 '13 at 14:26
Thanks everyone. Not sure why the previously asked question didn't show up in my initial search for an answer to this :/ — justclaire, May 28 '13 at 14:40

score 2 · Accepted Answer · edited May 23 '17 at 11:43

2

You can use var that = this; is order to keep a reference to current this object, when later this will be pointing to something else.

Example (taken from here):

$('#element').click(function(){
    // this is a reference to the element clicked on

    var that = this;

    $('.elements').each(function(){
        // this is a reference to the current element in the loop
        // that is still a reference to the element clicked on
    });
});

edited May 23 '17 at 11:43

Community

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answered May 28 '13 at 14:28

BobTheBuilder

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Same as my answer, but with an example, well played :) – ChrisCM May 28 '13 at 14:29

score 1 · Answer 2 · answered May 28 '13 at 14:26

1

Sometimes the meaning of this in JavaScript changes based on the scope. this inside of a constructor means something different than this inside of a function. Here's a good article about it.

answered May 28 '13 at 14:26

austin

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score 0 · Answer 3 · answered May 28 '13 at 14:27

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If you want access to "this" outside/inside of the scope of a specific function call where what "this" is may have changed. Just one example I can think of.

answered May 28 '13 at 14:27

ChrisCM

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What is the reasoning behind declaring var that = this; in javascript?

3 Answers3