Do you know what may cause memory leaks in JavaScript?

Question

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

Answer 1

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.

• JavaScript and memory leaks
• Introducing the closure
• More leakage patterns
• Conclusion

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.

Answer 2

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.

someElement->onclick->function-scope->elem->someElement

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;