A colleague of mine always sets their jQuery variables to null, to effectively dispose them, once they're finished with, e.g:

var bigThing = $(body);
// ...
// Do some stuff
// ...
bigThing = null;

Is that really necessary?

A colleague of mine always sets their jQuery variables to null, to effectively dispose them, once they're finished with, e.g:

var bigThing = $(body);
// ...
// Do some stuff
// ...
bigThing = null;

Is that really necessary?

• javascript
• jquery
• memory-management

• possible duplicate of Is it good practice to set variables to null when they are no longer needed? – Andy E Commented Jan 5, 2012 at 9:24
• Thanks, yes that question is very similar indeed and has an excellent answer. – Jay Commented Jan 9, 2012 at 16:20

5 Answers 5

If you encapsulate your code into functions thats unnecessary as after the function finishes the local variables will be killed anyway when no reference of them is used elsewhere.

Holding onto a selector/variable (caching) might have some positive effect tho if you need to select the same thing over and over again versus selecting it only once and keeping the variable.

Short answer: no that's hardly ever necessary if you're using jQuery.

It depends on what you did with it. If you didn't attach any event handlers to the DOM Node, the garbage collector will clear it when it's no longer referenced.

But even if you did attach event handlers, jQuery will take care of them in functions like .remove() and .empty() by detaching all event handlers for you. So as long as you use jQuery to interact with the DOM, you're safe.

Without jQuery, if you've attached an event handler to the Node, the GC won't clear it, even after you've removed the Node from the DOM tree and you no longer have any references to it. This is because the DOM Node contains a reference to a JavaScript object (i.e. the event handler) and vice versa. This creates a cyclic reference across two separate systems; something most garbage collectors have trouble with.

For further reading I point you to Douglas Crockford's article on Memory Leaks.

It's not necessary but good habit to remove reference and release the memory

Though not entirely necessary, this can be done to ensure that the GC clears it in its next run (which it'll anyway do for all allocations to which you don't have even 1 reference).

In your example though, the $(body) object (the jquery extended object, not the DOM body object) will be cleared if you set bigThing to anything else (not necessarily null)

Javascript has its own garbage collector. So, it appears that you don't need to explicitly dispose of the objects.

But due to various reasons, like bad implementation of garbage collector etc., it may happen that their are some memory leaks.

By nullifying them explicitly, you specify to the browser that this memory has to be cleared in next garbage collection.

In conclusion, though it is not necessary to do this, it will be a good practice to nullify the JQuery/javascript objects.