Package Exports

promisify-child-process

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Readme

promisify-child-process

seriously like the best async child process library

Based upon child-process-async, but more thorough, because that package doesn't seem very actively maintained.

promisify-child-process provides a drop-in replacement for the original child_process functions, not just duplicate methods that return a Promise. So when you call exec(...) we still return a ChildProcess instance, just with .then() and .catch() added to make it promise-friendly.

Install and Set-up

npm install --save promisify-child-process

If you are using a old version of Node without build-in Promises or Object.create, you will need to use polyfills.

Upgrading to v3

You must now pass maxBuffer or encoding to spawn/fork if you want to capture stdout or stderr.

Warning: capturing output

exec and execFile capture stdout and stderr by default. But spawn and fork don't capture stdout and stderr unless you pass an encoding or maxBuffer option:

const { spawn } = require('promisify-child-process');

async function() {
  // captures output
  const { stdout, stderr } = await spawn('ls', [ '-al' ], {encoding: 'utf8'});
  const { stdout, stderr } = await spawn('ls', [ '-al' ], {maxBuffer: 200 * 1024});

  // BUG, DOESN'T CAPTURE OUTPUT:
  const { stdout, stderr } = await spawn('ls', [ '-al' ]);
}

Usage

// OLD:
const { exec, spawn, fork, execFile } = require('child_process')
// NEW:
const { exec, spawn, fork, execFile } = require('promisify-child-process')

If for any reason you need to wrap a ChildProcess you didn't create, you can use the exported promisifyChildProcess function:

const {promisifyChildProcess} = require('promisify-child-process');

async function() {
  const { stdout, stderr } = await promisifyChildProcess(
    some3rdPartyFunctionThatReturnsChildProcess()
  )
}

Examples

`exec()`

async function() {
  const { stdout, stderr } = await exec('ls -al');
  // OR:
  const child = exec('ls -al', {});
  // do whatever you want with `child` here - it's a ChildProcess instance just
  // with promise-friendly `.then()` & `.catch()` functions added to it!
  child.stdin.write(...);
  child.stdout.pipe(...);
  child.stderr.on('data', (data) => ...);
  const { stdout, stderr } = await child;
}

`spawn()`

async function() {
  const { stdout, stderr, code } = await spawn('ls', [ '-al' ], {encoding: 'utf8'});
  // OR:
  const child = spawn('ls', [ '-al' ], {});
  // do whatever you want with `child` here - it's a ChildProcess instance just
  // with promise-friendly `.then()` & `.catch()` functions added to it!
  child.stdin.write(...);
  child.stdout.pipe(...);
  child.stderr.on('data', (data) => ...);
  const { stdout, stderr, code } = await child;
}