ECMAScript Harmony features in Node.js

Quick tip (via David Klassen): The following shell command lists all (highly experimental!) ECMAScript Harmony [1] features that can be switched on in Node.js.

    node --v8-options | grep harmony

For example, Node.js 0.10.2 supports:

--harmony_typeof	enable harmony semantics for typeof
--harmony_scoping	enable harmony block scoping
--harmony_modules	enable harmony modules (implies block scoping)
--harmony_proxies	enable harmony proxies
--harmony_collections	enable harmony collections (sets, maps, and weak maps)
--harmony	enable all harmony features (except typeof)

Note: “harmony semantics for typeof” is something that (unfortunately) had to be rejected for Harmony. It would have consisted of typeof null returning 'null', but that change would break too much existing code.

Reference:

1. ECMAScript: ES.next versus ES 6 versus ES Harmony