promise-worker-node

Modified version of promise-worker library to run on node.js. The original does work on node.js in general but is not designed to support it, and doesn't handle some error cases that could happen on node (which this library intends to handle).

A small and performant library for communicating with Web Workers, using Promises. Post a message to the worker, get a message back.

Goals:

• Tiny footprint (~2.5kB min+gz)
• Assumes you have a separate worker.js file (easier to debug, better browser support)
• JSON.stringifys messages for performance

Live examples:

• Web Workers

Usage

Install:

npm install promise-worker

Inside your main bundle:

// main.js
var PromiseWorker = require('promise-worker-node');
var worker = new Worker('worker.js');
var promiseWorker = new PromiseWorker(worker);

promiseWorker.postMessage('ping').then(function (response) {
  // handle response
}).catch(function (error) {
  // handle error
});

Inside your worker.js bundle:

// worker.js
var registerPromiseWorker = require('promise-worker-node/register');

registerPromiseWorker(function (message) {
  return 'pong';
});

Note that you require() two separate APIs, so the library is split between the worker.js and main file. This keeps the total bundle size smaller.

If you prefer script tags, you can get PromiseWorker via:

<script src="https://unpkg.com/promise-worker/dist/promise-worker.js"></script>

And inside the worker, you can get registerPromiseWorker via:

importScripts('https://unpkg.com/promise-worker/dist/promise-worker.register.js');

Message format

The message you send can be any object, array, string, number, etc.:

// main.js
promiseWorker.postMessage({
  hello: 'world',
  answer: 42,
  "this is fun": true
}).then(/* ... */);

// worker.js
registerPromiseWorker(function (message) {
  console.log(message); // { hello: 'world', answer: 42, 'this is fun': true }
});

Note that the message will be JSON.stringifyd, so you can't send functions, Dates, custom classes, etc.

Promises

Inside of the worker, the registered handler can return either a Promise or a normal value:

// worker.js
registerPromiseWorker(function () {
  return Promise.resolve().then(function () {
    return 'much async, very promise';
  });
});

// main.js
promiseWorker.postMessage(null).then(function (message) {
  console.log(message): // 'much async, very promise'
});

Ultimately, the value that is sent from the worker to the main thread is also stringifyd, so the same format rules apply.

Error handling

Any thrown errors or asynchronous rejections from the worker will be propagated to the main thread as a rejected Promise. For instance:

// worker.js
registerPromiseWorker(function (message) {
  throw new Error('naughty!');
});

// main.js
promiseWorker.postMessage('whoops').catch(function (err) {
  console.log(err.message); // 'naughty!'
});

Note that stacktraces cannot be sent from the worker to the main thread, so you will have to debug those errors yourself. This library does however, print messages to console.error(), so you should see them there.

Multi-type messages

If you need to send messages of multiple types to the worker, just add some type information to the message you send:

// main.js
promiseWorker.postMessage({
  type: 'en'
}).then(/* ... */);

promiseWorker.postMessage({
  type: 'fr'
}).then(/* ... */);

// worker.js
registerPromiseWorker(function (message) {
  if (message.type === 'en') {
    return 'Hello!';
  } else if (message.type === 'fr') {
    return 'Bonjour!';
  }
});

Browser support

This library is designed to run in Node.js, and is a fork of a library that does run in browsers. Technically this probably does run in browsers, but that's not the goal here. I'd recommend the original if you don't specifically need the extra node bits that this library adds.

API

Main bundle

new PromiseWorker(worker)

Create a new PromiseWorker, using the given worker.

• worker - the Worker or PseudoWorker to use.

PromiseWorker.postMessage(message)

Send a message to the worker and return a Promise.

• message - object - required
  • The message to send.
• returns a Promise

Worker bundle

Register a message handler inside of the worker. Your handler consumes a message and returns a Promise or value.

registerPromiseWorker(function)

• function
  • Takes a message, returns a Promise or a value.

Testing the library

First:

npm install

Then to test in Node (using an XHR/PseudoWorker shim):

npm test

Or to test manually in your browser of choice:

npm run test-local

Or to test in a browser using SauceLabs:

npm run test-browser

Or to test in PhantomJS:

npm run test-phantom

Or to test with coverage reports:

npm run coverage