ES6 (a.k.a. Harmony) Features Implemented in V8 and Available in Node

Recent version of V8 started to implement ES6 features and thus have become available in recent versions of Node, with a watershed moment when ES6 generator functions have become available in Node 0.11. This page is meant to track and list these features, and how to use them.

Promises (as of 0.11.13)

• Implicit API from the V8 test suite
• spec draft

Generators (--harmony_generators)

Collections (--harmony_collections sets, maps, and weak maps)

Proxies (--harmony_proxies)

• Implements the now obsolete, pre-ES6 Proxy spec.
• Use a shim such as harmony-reflect to patch the v8 Proxy object to follow the latest ES6 Proxy spec.

Modules (--harmony_modules)

Scoping (--harmony_scoping)

Observation (--harmony_observation)

Symbols (--harmony_symbols)

Iteration (--harmony_iteration)

String literals

Available in V8 as of 3.31.

Other

V8 flags; meaning and implications

// Flags for language modes and experimental language features.
DEFINE_bool(use_strict, false, "enforce strict mode")
DEFINE_bool(es_staging, false, "enable upcoming ES6+ features")

DEFINE_bool(harmony_typeof, false, "enable harmony semantics for typeof")
DEFINE_bool(harmony_scoping, false, "enable harmony block scoping")
DEFINE_bool(harmony_modules, false, "enable harmony modules (implies block scoping)")
DEFINE_bool(harmony_symbols, false, "enable harmony symbols (a.k.a. private names)")
DEFINE_bool(harmony_proxies, false, "enable harmony proxies")
DEFINE_bool(harmony_collections, false, "enable harmony collections (sets, maps)")
DEFINE_bool(harmony_generators, false, "enable harmony generators")
DEFINE_bool(harmony_iteration, false, "enable harmony iteration (for-of)")
DEFINE_bool(harmony_numeric_literals, false, "enable harmony numeric literals (0o77, 0b11)")
DEFINE_bool(harmony_strings, false, "enable harmony string")
DEFINE_bool(harmony_arrays, false, "enable harmony arrays")
DEFINE_bool(harmony_maths, false, "enable harmony math functions")
DEFINE_bool(harmony, false, "enable all harmony features (except typeof)")

DEFINE_implication(harmony, harmony_scoping)
DEFINE_implication(harmony, harmony_modules)
DEFINE_implication(harmony, harmony_symbols)
DEFINE_implication(harmony, harmony_proxies)
DEFINE_implication(harmony, harmony_collections)
DEFINE_implication(harmony, harmony_generators)
DEFINE_implication(harmony, harmony_iteration)
DEFINE_implication(harmony, harmony_numeric_literals)
DEFINE_implication(harmony, harmony_strings)
DEFINE_implication(harmony, harmony_arrays)
DEFINE_implication(harmony_modules, harmony_scoping)

DEFINE_implication(harmony, es_staging)
DEFINE_implication(es_staging, harmony_maths)

#A glimpse into the future (v8 3.29)

Iteration protocol.

Demonstrated here over a generator:

function *foo() {
    yield 1;
    yield 2;
    yield 3;
    yield 4;
    yield 5;
    return 6;
}

for (var v of foo()) {
    console.log( v );
}
// 1 2 3 4 5

Fat arrow functions (lambdas):

[1,2,3,4,5,6,7,8].map(x=>x*x).filter(x=>x%2)

// [ 1, 9, 25, 49 ]