Backlog rfcs/backlog/rfc-bun-bytecode.md

--bytecode flag — pre-compile JS to JSC bytecode at build

bun build --bytecode pre-compiles JS to JavaScriptCore bytecode and embeds it in the bundle. Cuts parse time at startup.

Summary

bun build --bytecode pre-compiles JS to JavaScriptCore bytecode and embeds it in the bundle. Cuts parse time at startup.

Why backlog

Patties build spec doesn't expose --bytecode today. There's no measured cold-start issue that justifies the added pipeline complexity.

Trigger to promote to draft

  • Edge adapter cold-start benchmarks show JS parse time as ≥ 20% of startup, OR
  • Single-binary deploy (--compile) latency-sensitive use case.

Bun-unique classification

Bun-only — as a user-facing build-time flag this doesn't exist on Node. Next.js can't ship the equivalent because V8 doesn't expose it that way.

Open questions when promoted

  • Source maps interaction — does --bytecode retain SourceMappingURL?
  • Per-target opt-in (bun adapter on, edge adapter off when target runtime doesn't support JSC bytecode) — likely Bun-target only.
  • Build-time cost vs runtime savings — measure before claiming.