esbuild-plugin-transform-ext

An esbuild plugin that transforms file extensions in bundled output, addressing esbuild's limitation of not being able to change extensions in the middle of the build process. Version 0.2.5 (current stable) is released under the MIT license. It allows defining per-pattern rules to map output extensions (e.g., .js to .cjs or .mjs) after esbuild's standard out-extension resolution, useful for dual CJS/ESM packages or mixed-format outputs. The plugin is lightweight, TypeScript-first with bundled types, and requires esbuild >=0.19.0 as a peer dependency. Compared to manual post-processing scripts, it integrates directly into esbuild's plugin pipeline without separate tooling.