bun-repl

bun-repl

Experimental unofficial REPL for Bun

Powered by Bun itself with the help of swc and JSC's ShadowRealm API

Install

bun add -g bun-repl
# alternatively now supports your package manager of choice
# (although only npm/npm-like have been tested)

Versioning

npm and GitHub releases will always be guaranteed to not rely on current Bun canary versions, but support for any version other than the latest non-canary will not be guaranteed.

The source code repository latest commit may contain code not yet in any release which depends on currently Bun canary-only features and has no guarantees.

Features

• Seamless JavaScript & TypeScript execution
• Single run CLI flags --eval and --print
• Top level import syntax supported (import fs from 'fs')
• Import either CommonJS or ESM local files and packages into the REPL
• Node.js REPL special underscore variables provided (_ and _error)
• Resistent to global object modification (output quality may decrease but never crash)
• Node.js repl module polyfill
• Persistent execution history (↑ ↓)
• REPL Commands (.command)

Usage

bun-repl [options]

Pass the -h or --help CLI option for a list of all options.

Type .help within the REPL for a list of commands.

Press ↑ and ↓ to travel up or down the execution history.

The repl module polyfill

bun-repl exposes a special variable repl which provides access to a REPL interface like the Node.js REPL (also accessible through import/require of repl or node:repl).

Currently only a subset of the node:repl API is implemented, see below:

• repl global object ✅
  • start() function ❌
  • writer() function ✅
    • options object ✅
  • repl property ❌
  • builtinModules array ✅
  • REPL_MODE_SLOPPY symbol ✅
  • REPL_MODE_STRICT symbol ✅
  • REPLServer class ❌
  • Recoverable class ❌

You can use repl.writer.options like you would in Node.js REPL to customize the live output of the running REPL.

Known issues & limitations

Please keep in mind this is unofficial and experimental software built on top of experimental software (Bun). Additionally, Bun will obviously be getting an official native REPL in the future which certainly will be much better, this module is merely serving as a temporary alternative until then.

PRs are welcome to help fix any of the items below or anything else.

• Top level await is not supported.
  • Reason: Usage of eval()
• Multi-line inputs are not supported.
  • Reason: The library used for prompts (rustybun) doesn't support this.
• To preserve lexically-scoped variables (let & const) across REPL runs, they need to be converted to var, which disrupts their behavior, especially const's (This also requires using non-strict mode)
  • Reason: Usage of eval() which has its own lexical scope.
• Attempting to run a non-file import while in a cwd without a node_modules folder has a small chance of crashing with a segfault.
  • Reason: A bug on Bun's side with automatic package installs and resolveSync.