At least for Chrome, all optimisation is disabled in functions containing a try/catch. It's probably similar for the other browsers. Try/catch combined with som

At least for Chrome, all optimisation is disabled in functions containing a try/catch. It's probably similar for the other browsers. Try/catch combined with some of the more sneaky semantics of javascript is rather a nightmare to optimise, I can imagine. Even a simple looking value can actually be a huge function chain (via defineProperty, defineGetter, or valueOf).