Bun research

Bun runtime module-resolution behavior relevant to TypeScript source execution.

Module resolution

Bun checks an explicit import path first. If that path is missing, it can try appended extensions and TypeScript-compatible substitutions. An import of ./value.js therefore loads value.js when present and can fall back to a matching TypeScript file when it is absent (runtime resolver).

For imports inside node_modules, Bun prefers JavaScript extensions over TypeScript extensions. Bun introduced that ordering because dependencies can ship TypeScript source that is not runnable by the consumer's toolchain (v1.0.14 rationale).