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node-bun

Node.js Compatibility Layer & Polyfills for Bun APIs

Highly experimental and unfinished

Goals

• Provide the ability to run programs and libraries written only for Bun in Node.js, for dual runtime support
• Remove the need for developers themselves to implement conditional feature usage based on runtime to support both Node.js and Bun
• Be functionality matching but not necessarily 1:1 identical, there will be quirks in some cases
• Implement beyond just the Bun global object, Bun specific properties added to the global object or process are included
• Implement Bun's built-in modules such as bun:jsc or bun:ffi
• Running TypeScript support & with Bun module resolution rules

Explicit Non-goals

• Replace Bun (Bun does much more than just runtime APIs + the many other reasons below)
• Match native Bun performance (simply not possible)
• Help run Node.js apps in Bun (Bun itself is already working on this, node-bun is only providing the other way around)
• Support Bun features beyond the runtime, such as CLI features like --hot (out of scope)
• Runtime features only accessible through Bun CLI, such as bun:test (out of scope)
• Implement Bun APIs not documented in bun-types (all assumed internal or unfinished thus not worthy of polyfill)
• Full CommonJS <-> ESM interop (some polyfills are simply not possible in CommonJS, so this is ESM only)
• Follow these lists literally, there may be occasional exceptions or changes towards both sides

Requirements

• Node.js 20.2+

Installation

npm i -g node-bun

Usage

The CLI is designed to act as a drop-in replacement to any Node.js command, by simply replacing node with node-bun

node-bun # display help
node-bun ./file.ts # same as `node ./file.js`
node-bun --info # node-bun specific flag will be passed to node-bun and not seen by Node.js
node-bun -v # valid Node.js flag will be passed to Node.js and not seen by node-bun

Versioning

node-bun's version will always try to match the closest Bun version that polyfills are supported for, if a new node-bun release is needed for the same Bun version, it will use a semver tag called rev (revision) as a fourth version number.

Example: 0.2.0 -> 0.2.1 -> 0.2.1-rev.1 -> 0.2.1-rev.2 -> 0.2.2 -> ...

The Bun.version and process.versions.bun properties are set to the node-bun version but with the rev tag stripped out.

Use process.versions.nodebun to get the unstripped version of node-bun that is running.

node-bun specific APIs

• process.versions.nodebun: {string} the version of node-bun in use
• process.isNodeBun: {1 | undefined} whether node-bun is in use or not, this is a number for parity with process.isBun