Cached this, jQuery

Question

I often see the code like this one:

$('.element').on('click', function(event) {
  var element = this;

  // somecode that uses "element"
});

Is there any reason to cache this?

`this` changes based on scope. So you may want to reference the original at some point. — Justin Wood, Dec 24 '13 at 18:29

score 2 · Accepted Answer · answered Dec 24 '13 at 18:30

This is necessary if the code contains a closure that needs to access this. this is not a local variable, so it will not be captured in the closure, you need to bind a local variable for that purpose.

You also need it if the code contains a loop using a function like $.each(), and the body of the loop needs to refer to the element. These functions rebind this in the body to the current iteration object.

score 2 · Answer 2 · edited Dec 24 '13 at 18:59

2

A lot of people set a reference to this if they need to reference it in another scope of code. For example:

$('.element').on('click', function(event) {
  var element = this;

  // somecode that users "element"
  function foo() {
      //$(this).text() WONT Work!
      alert($(element).text()); //references the element that was clicked
  }
});

edited Dec 24 '13 at 18:59

Fabrício Matté

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answered Dec 24 '13 at 18:32

jbarnett

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Object literal declaration does not change the `this` binding. Functions do. – Fabrício Matté Dec 24 '13 at 18:34
You could've used `{ text: function() { return $(this).text(); } }` in the object literal example but well, either way the example is more correct now. Just fix the "this references foo" part which you left behind. `=]` – Fabrício Matté Dec 24 '13 at 18:43
Good catch! Updated code. – jbarnett Dec 24 '13 at 18:45
I mean, the comment "this references foo" from your first example does not apply to your new example. The `this` binding for a `foo()` invocation would be `window` (or `null` in strict mode). – Fabrício Matté Dec 24 '13 at 18:47

score 1 · Answer 3 · answered Dec 24 '13 at 18:30

1

Once you are inside a function or loop, this might refer to an object within that function. Therefor explicity assigning the element allows you to always access it, independent of the scope.

answered Dec 24 '13 at 18:30

Neograph734

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score 0 · Answer 4 · answered Dec 24 '13 at 18:30

0

this is not a jQuery element, wrap it in $(this).

Caching is good because it stores the element, and it doesn't take up memory or processing time trying to re-find the element. However, this changes on scope so you might not want to cache that one.

answered Dec 24 '13 at 18:30

Sterling Archer

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Cached this, jQuery

4 Answers4