This release corresponds to RN 0.75.

This release comes with many bug fixes, language features (WeakRef & BigInt), and also the removal of the debugger on the command line tools. This means much better performance when using Hermes from the CLI. In addition, RN now builds Hermes from source, so we no longer need to publish specific versions of Hermes to target a specific version of RN.

In preparation for the 0.68.x, this release brings numerous bug fixes and performance improvements to Hermes.

In preparation for the release of RN0.67, this release brings numerous bug fixes and performance improvements to Hermes.

This release is primarily made to close the gap between the Hermes cut and the (upcoming) React Native 0.66 cut. Among the ~400 commits, we kept delivering memory and size wins, bugfixes, and made other progress behind the scene.

In preparation for the RN 0.65 stable release, several refinements had been made upon v0.8.0:

• Hermes on iOS now supports Apple M1 Macs (ARM64 simulators) and Mac Catalyst! Thanks to #546 and #475.
• A special directive "show source" is introduced to make Function.prototype.toString returning original source code to support the source code injecting use cases e.g. #114.
• Critical bug fixes e.g. #513 and #537.

This is a release candidate targeting the upcoming RN 0.65 release.

Highlighted Changes

• A new concurrent garbage collector "Hades", which delivered up to 30x shorter GC pause time on 64-bit device and 14x shorter on 32-bit devices. At Facebook, we saw this improve some CPU-intensive workloads by 20%-50%. You can learn more about Hades here.
• ECMAScript Internationalization API Specification (ECMA-402, or Intl) was a long asking features #23 (comment). It is now built into Hermes on Android and enabled by default, with only 57-62K per API size overhead (compared to JSC's 6MiB). With this change, Hermes users no longer require locale polyfills. A big thank you to @mganandraj and other partners at Microsoft for driving the implementation to make this happen!
• Memory Improvements including SMI (Small Integer) and pointer compression that shrank the JavaScript heap by 30%
• Changes to Function.prototype.toString that fixed performance drop due to improper feature detection: #471 (comment)

This release includes miscellaneous fixes to support the road to RN 0.64.

This release adds macOS ARM64 support to 0.5.x branch for RN macOS v0.63.x (#390 by @alloy).

NOTE: this release is only available for the Darwin platform (i.e. this version only exists at hermes-engine-darwin but not hermes-engine). Please use 0.5.1 or 0.5.2-rc1 (with Proxy enabled) for other platforms.

This is (still) a pre-release driven by community PRs to support using Hermes on more platforms at RN 0.64. Noted that ongoing from this release, we will publish hermes-runtime-darwin to the CocoaPod in place of publishing hermes-engine-darwin to NPM.