I'm viewing my page, and whenever I scroll, a 0.5 - 1 seconds lag happens. Not even hover CSS executes. Obviously a JavaScript function holds, but how to track it down? I can't provide any code as it's a very big codebase, I'm using Chrome / Firefox.
You can use the Performance-Tab in the Chrome Dev Tools to record events & everything else. Then looking at the call tree, you can see what events & functions slow down your site easily.