Friday, June 9, 2017

V8 Release 6.0

Every six weeks, we create a new branch of V8 as part of our release process. Each version is branched from V8’s git master immediately before a Chrome Beta milestone. Today we’re pleased to announce our newest branch, V8 version 6.0, which will be in beta until it is released in coordination with Chrome 60 Stable in several weeks. V8 6.0 is filled with all sorts of developer-facing goodies. We’d like to give you a preview of some of the highlights in anticipation of the release.


V8 6.0 introduces support for SharedArrayBuffer, a low-level mechanism to share memory between JavaScript workers and synchronize control flow across workers. SharedArrayBuffers give JavaScript access to shared memory, atomics, and futexes. SharedArrayBuffers also unlock the ability to port threaded applications to the web via asm.js or WebAssembly.

For a brief, low-level tutorial, see the spec tutorial page or consult the Emscripten documentation for porting pthreads.

Object rest/spread properties

This release introduces rest properties for object destructuring assignment and spread properties for object literals. Object rest/spread properties are Stage 3 features.

Spread properties also offer a terse alternative to Object.assign() in many situations.

// Rest properties for object destructuring assignment:
const person = {
  firstName: 'Sebastian',
  lastName: 'Markbåge',
  country: 'USA',
  state: 'CA',
const { firstName, lastName, } = person;
console.log(firstName); // Sebastian
console.log(lastName); // Markbåge
console.log(rest); // { country: 'USA', state: 'CA' }

// Spread properties for object literals:
const personCopy = { firstName, lastName, };
// { firstName: 'Sebastian', lastName: 'Markbåge', country: 'USA', state: 'CA' }

For more information, see the usage post on Web Fundamentals.

ES6 Performance

V8 6.0 continues to improve performance of ES2015 features. This release contains optimizations to language feature implementations that overall result in a roughly 10% improvement in V8’s ARES-6 score.


Please check out our summary of API changes. This document is regularly updated a few weeks after each major release.

Developers with an active V8 checkout can use 'git checkout -b 6.0 -t branch-heads/6.0' to experiment with the new features in V8 6.0. Alternatively you can subscribe to Chrome's Beta channel and try the new features out yourself soon.

Posted by the V8 team


  1. Will shared memory be enabled by default?

  2. Awesome. So what is are6 testing exactly?

    Where can i find v8 perf benchmarking results? I'd like to track how it compares to previous versions.