Very cool, but there are some corner cases missing (other than the ones explicitly left as an exercise for the reader): while it is currently strictly true that

Very cool, but there are some corner cases missing (other than the ones explicitly left as an exercise for the reader): while it is currently strictly true that only functions create new scopes, if you're not using strict mode, the "with" statement will also create a new scope. And eventually you'll have to start worrying about block-scoping of "let" statements.