I really hope that Map and Set will be iterable as described here: http://wiki.ecmascript.org/doku.php?id=harmony:iterators http://wiki.ecmascript.org/doku.php?

I really hope that Map and Set will be iterable as described here: http://wiki.ecmascript.org/doku.php?id=harmony:iterators http://wiki.ecmascript.org/doku.php?id=harmony:iterators otherwise, in my opinion, they will be pretty useless. As an addendum it looks like that 'undefined' is a valid key: var m = new Map; m.set(undefined, 1); console.log(m.get(undefined));