> if I need a specific version of specific browsers (which it is) No, you don't need a specific browser. You can polyfill it. (The reference implementation is

> if I need a specific version of specific browsers (which it is) No, you don't need a specific browser. You can polyfill it. (The reference implementation is a polyfill.) If you want the performance benefits, you'll need to update your browser. But that's true for JavaScript in general. IE8's engine is very slow, for example. Only the most recent browsers can offer the best performance.