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 6.1, which is in beta until its release in coordination with Chrome 61 Stable in several weeks. V8 v6.1 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.
In addition to that, work continued on the performance of other language features. For example, the Object.prototype.isPrototypeOf method, which is important for constructor-less code using mostly object literals and Object.create instead of classes and constructor functions, is now always as fast and often faster than using the instanceof operator.
Function calls and constructor invocations with variable number of arguments also got significantly faster. Calls made with Reflect.apply and Reflect.construct received an up to 17× performance boost in the latest version.
Array.prototype.forEach is now inlined in TurboFan and optimized for all major non-holey elements kinds.
Binary size reduction
The V8 team has completely removed the deprecated Crankshaft compiler, giving a significant reduction in binary size. Alongside the removal of the builtins generator, this reduces the deployed binary size of V8 by over 700 KB, depending on the exact platform.
asm.js is now validated and compiled to WebAssembly
If V8 encounters asm.js code it now tries to validate it. Valid asm.js code is then transpiled to WebAssembly. According to V8’s performance evaluations, this generally boosts throughput performance. Due to the added validation step, isolated regressions in startup performance might happen.
Please note that this feature was switched on by default on the Chromium side only. If you are an embedder and want to leverage the asm.js validator, enable the flag –validate-asm.
When debugging WebAssembly, it is now possible to display local variables in DevTools when a breakpoint in WebAssembly code is hit.
Please check out our summary of API changes. This document is regularly updated a few weeks after each major release.