[sahrens2012]

Proof is in the pudding: 28% startup speed improvement in MS Office for Android vs V8 with bytecode caching (so AOT compiling the bytecode isn’t a big advantage specific to Hermes):

https://news.ycombinator.com/item?id=20413046

The key is that Hermes is optimized for a totally different environment and workload - RN apps from disk on slow Android devices vs. websites downloaded on desktop computers.

The fact that Hermes is architected for RN from the beginning is key. Bytecode is as compact as possible, and is mmap’d. mmap’d bytecode is a very deep change with huge benefits, but also limits some optimizations other engines rely on, such as inline caching.

Also note Hermes does not have a JIT to save memory and APK size. A lot of the heroic perf work in V8/JSC is in the JIT which is not useful in most RN scenarios/environments.