According to Facebook, there's no plan to push Hermes' beyond React Native to Node.js or to turn it into the foundation of a Facebook-branded browser. That's because it's optimized for mobile apps and wouldn't offer advantages over other engines in other usage scenarios.
The reason Hermes exists, as Facebook tells it, is to make React Native better. "Hermes allows for more optimization on mobile since developers control the build stack," said a Facebook spokesperson in an email to The Register. "For example, we implemented bytecode precompilation to improve performance and developed more efficient garbage collection to reduce memory usage."
Facebook, a company spokesperson said, is planning to publish benchmark figures to support its performance claims next week. In a discussion on Hacker News, Microsoft developer Andrew Coates claims that internal testing of Hermes and React Native in conjunction with Microsoft Office for Android shows TTI using Hermes at 1.1s, compared to 1.4s for V8, and with 21.5MB runtime memory impact, compared to 30MB with V8.
A developer who works for a Facebook rival told The Register that the success of Hermes will remain tied to the success of React Native unless it gets taught how to compile to platforms other than Android. And for the foreseeable future, browsers can be expected to continue to use runtimes based on C++ for reasons of performance and portability. ®