November 24, 2025 · tmikov
Big news for Hermes JSON parsing. Michael from our team worked on speeding it up for the last month - the result is between 2.7x-3.4x faster! It is available in the static_h branch now and will be included in the next stable releases.
Incomplete list of improvements:
- Switch to an iterative parser
- Cache object hidden classes
- Optimize string parsing
- Use @lemire's fast_float
- Add an even faster number path for integers
- Avoid unnecessary allocations
- Use a per-character lookup and function dispatch table
Coming up next: JSON.stringify().