How do browsers detect a JS script is not responding?

Question

Sometimes in web development the browser warns that some js script is not responding. We generally call that a freeze effect. I generally work around it by being less aggressive in term of data size or client-side processing. But I don't really know how the most popular browsers detect this. Is it based on memory consumption or kind of timeout? Is there any tool to measure that?

Answer 1

It's mainly timeouts-based detection. In Firefox timeouts are user-defined, http://kb.mozillazine.org/Unresponsive_Script_Warning

IE decides that script isn't responding after 5 billion executed JS statements.

For more information you could check out this article: http://www.nczonline.net/blog/2009/01/05/what-determines-that-a-script-is-long-running/