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

Bun.Transpiler — on-demand single-file TS/TSX transpile

Bun.Transpiler returns a transpiler instance that runs TS→JS / JSX→JS per file without wrapping into a build graph. Faster than SWC for many workloads; sync …

Summary

Bun.Transpiler returns a transpiler instance that runs TS→JS / JSX→JS per file without wrapping into a build graph. Faster than SWC for many workloads; sync API.

Why backlog

Bun.build already handles transpile end-to-end for our build, dev-bundler (spec 18), and edge adapter. There is no current spec slot for raw per-file transpile.

Trigger to promote to draft

A feature appears that needs file-level transpile decoupled from bundling — e.g. an eval/REPL endpoint, a custom dev tool, or a plugin that wants to transpile arbitrary user-supplied source.

Bun-unique classification

Bun-faster — Node has SWC (via @swc/core) and Babel; Bun's transpiler is materially faster but capability is not new.

Open questions when promoted

  • Does the transpiler need to share macro/import-attribute config with Bun.build?
  • Would we expose it through a plugin hook or a direct framework API?