Chromium Blog: The Future of JavaScript

Chromium Blog

News and developments from the open source browser project

The Future of JavaScript – take a peek today!

Friday, February 10, 2012

Harmonydev channel

Lexical scoping. Now "let" is the new "var" – traditional "var" declarations are complemented with "let" and "const". Both are properly block-scoped bindings, eliminating a common source of errors and weird behaviour. Function declarations are now officially allowed in local scope as well, and also obey lexical scoping. (Note: Lexical scoping is only available in ES strict mode.)

Collections. Efficient maps and sets will make your life easier. Any value can be used as a key or element, including objects. No surprises, no more need to abuse objects as dictionaries. (Caveat: Iteration over collections is not yet specified.)

Weak maps. A special kind of map for which the garbage collector determines when a key is no longer reachable, so that the key-value pair can be removed from the map automatically. This goes a long way towards avoiding memory leaks in long-lived tables and relieves the developer from worrying about stale entries.

Proxies. A proxy simulates a JavaScript object or function, and can customize just about any aspect of their behaviour that you can imagine. This is a real power feature, that takes reflection to a new level and can be used to implement various advanced abstractions and interfaces.