[removed] should I worry about memory leaks in 2011?

Question

The topic of memory leaks in JavaScript is not brought up often. However, I stumbled upon this article, written in 2007. The authors state:

Internet Explo

Answer 1

NO.

More complete answer: maybe. The fact you are asking so vaguely is a strong signal that you personally are unlikely to need to worry.

In practice, the vast majority of JavaScript code simply doesn't worry about it, and doesn't need to worry about it because only in particular circumstances do memory leaks in pages end up affecting users. The browser and frameworks cover your arse pretty well.

There are only a few questions you need to answer:

Q: Are you supporting a rich single page application that uses JavaScript heavily?

If not, then don't waste your time worrying. If you (or your QA, or your clients) find a memory over-usage issue with a page then fix it when it comes up.

Q: Do you need to support mobile devices, and you have heavy javascript usage?

Mobile devices have limited memory and extra care needs to be taken.

If you ARE developing a JavaScript heavy application, and you need to worry about memory usage, then...

The issue of "dirty" references to objects that cause JavaScript objects and DOM objects to never get garbage collected is important to certain types of JavaScript applications. Caches that grow forever, unexpected global references, and unexpected references inside closures can be a problem.

The Heap Snapshot tool in Chrome's Web Inspector can help.

Here is a git project that has a useful writup and walks the javascript objects it can: https://github.com/tlrobinson/leakhelper

There are other tools that help you, but I wrote my own over time: 1. our framework marks deleted widgets, so I wrote code to walk all arrays and objects from window or document looking for the paths to delected objects (javascript code can't walk closures but it definitely helped find some leaks). 2. Another trick I used was when widget x was deleted, I do a x.leakhelper = window.createElement('leakhelper') and setAttribute the oid of the widget, but not add the element into the document. If the DOM element is not garbage collected then the widget must have a dangling reference to it somewhere. In IE use window.collectGarbage() to force the GC, and use sIEve to detect the leaked DOM element (I found sIEve to be really useful).

Obsolete question: Do you need to strongly support either IE6 or IE7 AND you use JavaScript heavily? Most of the scary leaks you used to read about only occur in < IE8. If you are supporting IE6 or IE7 then you need good luck and perseverence (all frameworks leak, and it is hard to write code that doesn't even with a perfect framework - I ended up writing my own IE leak prevention code for our production use for IE6/7 users). The IE6/IE7 leaks can last even after you close your page - which is why they are so nasty.