The first step in the V8 release process is a new branch from the git master immediately before Chromium branches for a Chrome Beta milestone (roughly every six weeks). Our newest release branch is V8 5.0, which will remain in beta until we release a stable build in conjunction with Chrome 50 Stable. Here’s a highlight of the new developer-facing features in this version of V8.
Note: The version number 5.0 does not carry semantic significance or mark a major release (as opposed to a minor release).
Improved ECMAScript 2015 (ES6) support
V8 v5.0 contains a number of ES2015 features related to regular expression (regex) matching.
RegExp Unicode flag
The RegExp Unicode flag,
u, switches on a new Unicode mode for regular expression matching. The Unicode flag treats patterns and regex strings as a series of Unicode codepoints. It also exposes new syntax for Unicode codepoint escapes.
u flag also makes the
. atom (also known as the single character matcher) match any Unicode symbol rather than just the characters in the Basic Multilingual Plane (BMP).
const string = 'the 🅛 train';
RegExp customization hooks
ES2015 includes hooks for RegExp subclasses to change the semantics of matching. Subclasses can override methods named
Symbol.split in order to change how RegExp subclasses behave with respect to
String.prototype.match and similar methods.
Performance improvements in ES2015 and ES5 features
Release 5.0 also brings a few notable performance improvements to already implemented ES2015 and ES5 features.
The implementation of rest parameters is 8-10x faster than that of the previous release, making it more efficient to gather large numbers of arguments into a single array after a function call.
Object.keys, useful for iterating over an object’s enumerable properties in the same order returned by
in, is now approximately 2x faster.
Please check out our summary of API changes. This document gets regularly updated a few weeks after each major release.
Developers with an active V8 checkout can use
git checkout -b 5.0 -t branch-heads/5.0 to experiment with the new features in V8 5.0. Alternatively you can subscribe to Chrome's Beta channel and try the new features out yourself soon.