See harmony for requirements, goals, and means informing and guiding the proposals under development for ES-Harmony.

Lacking a formal language specification, the following list is not definitive, but it should reflect consensus achieved so far in TC39. Anything can be revisited for a good reason, of course.

The following list will grow, but not without bound before the next ECMA-262 Edition is constructed. Without prematurely triaging or using “ES6” (which might have to be used for a short-term edition, worst-case), for now let’s focus on near-term proposals while keeping important longer-term strawman proposals warm.

— Brendan Eich 2009/07/29 23:51

• Block scoped bindings (markm):
  • let, the new var but block-scoped and with better use-before-set semantics (dherman,markm)
  • const, for constant let-like bindings (dherman,markm)
  • block functions, let-scoped functions declared directly in block statements (markm)
• destructuring assignment and binding declaration forms, based on object and array initialiser syntax (allen)
• parameter default values, supplying default arguments to trailing optional parameters (allen)
• rest parameters, for a trailing formal parameter capturing variable actual arguments as an array (allen)
• spread, the ... prefix operator for expanding an array actual parameter into its elements (allen)
• proxies, a “catchall” mechanism for intercepting property accesses genericallya (tomvc)
  • proxies_semantics, explains the semantics in terms of the ES5 spec’s internal operations (tomvc)
  • extended object api standardizing some “missing” ES5 methods on Object. (tomvc)
• weak maps non-enumerable object-identity-based tables. Fixes a crucial memory leak in conventional weak-key tables. (markm)