tinyspawn

tinyspawn is a minimalistic child_process wrapper with following features:

• Small (~80 LOC, 835 bytes).
• Focus on performance.
• Zero dependencies.
• Meaningful errors.
• Easy to extend.
• Fully typed.

Install

$ npm install tinyspawn --save

Usage

Getting started

The child_process in Node.js is great, but I always found the API confusing and hard to remember.

That's why I created tinyspawn. It's recommended to bind it to $:

const $ = require('tinyspawn')

The first argument is the command (with arguments) to be executed:

const { stdout } = await $(`node -e 'console.log("hello world")'`)
console.log(stdout) // => 'hello world'

The second argument is any of the spawn#options:

const { stdout } = $(`node -e 'console.log("hello world")'`, {
  shell: true
})

When you execute a command, it returns a ChildProcess instance:

const {
  signalCode,
  exitCode,
  killed,
  spawnfile,
  spawnargs,
  pid,
  stdin,
  stdout,
  stderr,
  stdin
} = await $('date')

Piping streams

Since tinyspawn returns a ChildProcess instance, you can use it for interacting with other Node.js streams:

const subprocess = $('echo 1234567890')
subprocess.stdout.pipe(process.stdout) // => 1234567890

/* You can also continue interacting with it as a promise */

const { stdout } = await subprocess
console.log(stdout) // => 1234567890

or stdin:

const { Readable } = require('node:stream')

const subprocess = $('cat', { stdin: 'hello world' })
Readable.from('hello world').pipe(subprocess.stdin)
const {stdout} = await subprocess

console.log(stdout) // 'hello world'

JSON parsing

A CLI program commonly supports a way to return a JSON that makes it easy to connect with other programs.

tinyspawn has been designed to be easy to work with CLI programs, making it possible to call $.json or pass { json: true } as an option:

const { stdout } = await $.json(`curl https://geolocation.microlink.io`)

Extending behavior

Although you can pass spawn#options as a second argument, sometimes defining something as default behavior is convenient.

tinyspawn exports the method $.extend to create a tinyspawn with spawn#options defaults set:

const $ = require('tinyspawn').extend({
  timeout: 5000,
  killSignal: 'SIGKILL'
})

Meaningful errors

When working with CLI programs and something wrong happens, it's crucial to present the error as readable as possible.

tinyspawn prints meaningful errors to help you understa dn what happened:

const subprocess = $('node', ['child.js'], {
  timeout: 500,
  killSignal: 'SIGKILL'
})

console.log(await subprocess.catch(error => error))
// Error [ChildProcessError]: The command spawned as:

//   `node child.js`

// exited with:

//   `{ signal: 'null', code: 1 }`

// with the following trace:

//     at createChildProcessError (/Users/kikobeats/Projects/microlink/tinyspawn/src/index.js:20:17)
//     at ChildProcess.<anonymous> (/Users/kikobeats/Projects/microlink/tinyspawn/src/index.js:63:18)
//     at ChildProcess.emit (node:events:531:35)
//     at ChildProcess._handle.onexit (node:internal/child_process:294:12) {
//   command: 'node child.js',
//   connected: false,
//   signalCode: null,
//   exitCode: 1,
//   killed: false,
//   spawnfile: 'node',
//   spawnargs: [ 'node', 'child.js' ],
//   pid: 63467,
//   stdout: '',
//   stderr: 'node:internal/modules/cjs/loader:1148\n' +
//     '  throw err;\n' +
//     '  ^\n' +
//     '\n' +
//     "Error: Cannot find module '/Users/kikobeats/Projects/microlink/tinyspawn/child.js'\n" +
//     '    at Module._resolveFilename (node:internal/modules/cjs/loader:1145:15)\n' +
//     '    at Module._load (node:internal/modules/cjs/loader:986:27)\n' +
//     '    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:174:12)\n' +
//     '    at node:internal/main/run_main_module:28:49 {\n' +
//     "  code: 'MODULE_NOT_FOUND',\n" +
//     '  requireStack: []\n' +
//     '}\n' +
//     '\n' +
//     'Node.js v20.15.1'
// }

The ChildProcess instance properties are also available as part of the error:

const { stdout: node } = await $('which node')

const error = await $(`${node} -e 'require("notfound")'`).catch(error => error)

const {
  signalCode,
  exitCode,
  killed,
  spawnfile,
  spawnargs,
  pid,
  stdin,
  stdout,
  stderr,
  stdin
} = error

License

tinyspawn © microlink.io, released under the MIT License.
Authored and maintained by Kiko Beats with help from contributors.

microlink.io · GitHub microlink.io · Twitter @microlinkhq