[btilly]

If we implement the suggested fix, and then someone evals code in that scope, they can get the surprising result that variables which look like they should be in scope actually aren't. Careful analysis of this will have many edge cases to worry about.

Implementing the simplest thing that is correct according to the spec sounds like a good idea to me.

[glasser]

Yes, but you can statically determine whether or not eval is called.

A world-class JavaScript environment like V8 is far past "the simplest thing that is correct according to the spec".

In fact, the JavaScript spec doesn't actually define anything about garbage collection! You can create a compliant ECMAScript-262 runtime that literally never collects any garbage ever. That's certainly the simplest correct thing. But it's a bad idea!

V8 already goes to the trouble of figuring out whether or not a given variable needs to be stored in the lexical environment or not. Specifically: variables that are not used in ANY closures and where there is no eval in sight can be stored outside of the lexical environment. This is great, and better than many similar programming language environments offer.

It just would be even better if they went one step farther.

[btilly]

V8 attempts to be fast. There is a trade-off between sophisticated analysis during compilation, and page performance.

I'm not as convinced as you that they haven't found the right balance.