author: ‘Clemens Hammacher, compiler wrangler’

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 7.3, which is in beta until its release in coordination with Chrome 73 Stable in several weeks. V8 v7.3 is filled with all sorts of developer-facing goodies. This post provides a preview of some of the highlights in anticipation of the release.

Async stack traces

We are turning on the --async-stack-traces flag by default. Zero-cost async stack traces make it easier to diagnose problems in production with heavily asynchronous code, as the error.stack property that is usually sent to log files/services now provides more insight into what caused the problem.

Faster await

Related to the above-mentioned --async-stack-traces flag, we’re also enabling the --harmony-await-optimization flag by default, which is a prerequisite for the --async-stack-traces. See faster async functions and promises for more details.

Faster Wasm startup

Via optimizations to the internals of Liftoff, we improved WebAssembly compilation speed significantly without regressing the quality of the generated code. For most workloads, compilation time reduced by 15–25%.

Liftoff compile time on the Epic ZenGarden demo

JavaScript language features

V8 v7.3 comes with several new JavaScript language features.

Object.fromEntries

The Object.entries API is nothing new:

  1. const object = { x: 42, y: 50 };
  2. const entries = Object.entries(object);
  3. // → [['x', 42], ['y', 50]]

Unfortunately, there’s no easy way to go from the entries result back to an equivalent object… until now!
V8 v7.3 supports Object.fromEntries(), a new built-in API that performs the inverse of Object.entries:

  1. const result = Object.fromEntries(entries);
  2. // → { x: 42, y: 50 }

With both Object.entries and Object.fromEntries in the language, it’s now easier than ever to convert between Maps and ordinary objects in JavaScript.

String.prototype.matchAll

A common use case of global (g) or sticky (y) regular expressions is applying it to a string and iterating through all of the matches. The new String.prototype.matchAll API makes this easier than ever before, especially for regular expressions with capture groups:

  1. const string = 'Favorite GitHub repos: tc39/ecma262 v8/v8.dev';
  2. const regex = /\b(?<owner>[a-z0-9]+)\/(?<repo>[a-z0-9\.]+)\b/g;
  3. for (const match of string.matchAll(regex)) {
  4.  console.log(`${match[0]} at ${match.index} with '${match.input}'`);
  5.  console.log(`→ owner: ${match.groups.owner}`);
  6.  console.log(`→ repo: ${match.groups.repo}`);
  7. }
  8. // Output:
  9. //
  10. // tc39/ecma262 at 23 with 'Favorite GitHub repos: tc39/ecma262 v8/v8.dev'
  11. // → owner: tc39
  12. // → repo: ecma262
  13. // v8/v8.dev at 36 with 'Favorite GitHub repos: tc39/ecma262 v8/v8.dev'
  14. // → owner: v8
  15. // → repo: v8.dev

For more details, read our Web Fundamentals article on String.prototype.matchAll.

Atomics.notify

Atomics.wake has been renamed to Atomics.notify, matching a recent spec change.

V8 API

Please use git log branch-heads/7.2..branch-heads/7.3 include/v8.h to get a list of the API changes.
Developers with an active V8 checkout can use git checkout -b 7.3 -t branch-heads/7.3 to experiment with the new features in V8 v7.3. Alternatively you can subscribe to Chrome’s Beta channel and try the new features out yourself soon.