Do you know what may cause memory leaks in JavaScript?

Do you know what may cause memory leaks in JavaScript?
I am interested in browsers: IE 7, FireFox 3, Safari 3

There is a nice article about JavaScript and memory leaks. It does not specific about on browser, it rather describes the whole problematic of memory leaks and JavaScript.

I think it is a better approach to be as browser unspecific as possible insted of optimizing for a few browsers, when developing a website for the public.

Here is a classic memory leak in IE:-

function body_onload()
    var elem = document.getElementById('someElementId');
    // do stuff with elem
    elem.onclick = function() {
        //Some code that doesn't need the elem variable

After this code has run there is circular reference because an element has a function assigned its onclick event which references a scope object which in turn holds a reference to element.


In IE DOM elements are COM based reference counting objects that the Javascript GC can’t cleanup.

The addition of a final line in the above code would clean it up:-

var elem = null;

In general; circular references are the cause of many problems.
I remember IE 6 (not sure if it applies to 7) leaking quite badly with XMLHTTP… setting onreadystatechange = null once it was finished with fixed it.

You’re dealing with 2 kinds of objects (and 2 garbage collectors), javascript and DOM objects, which can reference each other (the circular reference), and then neither GC can take care of all its objects even when the page unloads. Here’s a good description:

Read More:   In node.js, how to declare a shared variable that can be initialized by master process and accessed by worker processes?

You can check this MSDN article for Internet Explorer memory leak patterns. Also there are some tools for detecting memory leaks:

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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