webworker-promise

A small promise based wrapper over the "webworkers"

Usage

Install:

npm install webworker-promise

Inside your main bundle:

// main.js
const WebworkerPromise = require('webworker-promise');
const worker = new WebworkerPromise(new Worker('worker.js'));

worker
  .postMessage('ping')
  .then((response) => {
    // handle response
  })
  .catch(error => {
    // handle error
  });

Inside worker.js:

// worker.js
const registerWebworker = require('webworker-promise/lib/register');

registerWebworker(async (message, emit) => {
  //message - ping
  return 'pong';
});

Nodejs

You can use webworker-promise with nodejs using shim

Note It uses nodejs child_process for workers

const Worker = require('webworker-promise/lib/node-worker');
const WebWorkerPromise = require('webworker-promise');

const worker = new WebWorkerPromise(new Worker('./node-process'));

Message format

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

// main.js
worker.postMessage({
  hello: 'world'
}).then(/* ... */);

// worker.js
registerWebworker(async (message, emit) => {
  console.log(message); // { hello: 'world'}
});

Note that you can't send dom objects via postMessage

Transferable

You can use transferable list for performance issue

Send just arraybuffer

worker.postMessage(arrayBuffer, [arrayBuffer])

Or inside objects

worker.postMessage({myArr: arrayBuffer, myArr2: arrayBuffer2}, [arrayBuffer, arrayBuffer2]);

And in worker.js

registerWebworker(async (message, emit) => {
  return new registerWebworker.TransferableResponse(arrayBuffer, [arrayBuffer]);
});

Events

You can send events from worker to main-process

// main.js
worker.postMessage('ping', [], (eventName, data) => {
  eventName; // hello
  data; // world
})
.then(response => {
  //job end
  //pong
})

// worker.js
registerWebworker(async (message, emit) => {
  emit('hello', 'world');
  return 'pong';
});

EventEmitter

You can use it as regular event-emitter, webworker-promise has all event-emitter methods to send events in direction worker => main or main => worker

// main.js

host.on('add:ok', (sum) => {
// sum is 33;
});

worker.emit('add', 11, 22);

// worker.js
const host = registerWebworker()
.on('add', (n1, n2) => {
    host.emit('add:ok', n1 + n2);
})
.once('minus', (n1, n2) => {
  host.emit('minus:answer', n1 - n2);
})
// you still can add operations
.operation('foo', async () => {
  return 'bar';
});

Operations

Also, you can create operations

// worker.js
registerWebworker(async (message) => {
  //handle postMessage
  return 'pong';
})
.operation('hello', async (message, emit) => {
  return 'world';
});

// main.js
worker.exec('hello')
.then(response => {
  // world
})

Workers Pool

Dynamic pool for workers.

Note: It's experimental feature, and api may be changed

const WorkerPool = require('webworker-promise/lib/pool');
const pool = WorkerPool.create({
    src: './test.worker.js',
    // or
    create: () => new Worker('./test.worker.js'),
    maxThreads: 3, // optional, default is 2, max numbers of workers to create if necessary
    maxConcurrentPerWorker: 1 // optional, default is 1
});

pool.postMessage('hello')
    .then(() => {
        console.log('result');
    });

Pool has exec and postMessage methods with the same api as WebWorkerPromise

Promises

Inside of the worker, the registered handler should return Promise or just value

Error handling

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

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

// main.js
worker.postMessage('hi').catch(function (err) {
  console.log(err.message); // 'myException!'
  console.log(err.stack); // stack trace string
});

Note that stacktraces cannot be originaly sent from the worker to the main thread, so you're getting just string stack trace

Browser support

• Chrome
• Firefox
• Safari 8+
• IE 10+
• Edge
• iOS 8+
• Android 4.4+

---

Main bundle

new WebworkerPromise(worker)

Create a new WebworkerPromise, using the given worker.

• worker - the Worker to use.

PromiseWorker.postMessage(message, transferableList, onEvent)

Send a message to the worker and return a Promise.

• message - object - required
  • The message to send.
• transferable - transferable list
• onEvent - on-event callback function to handle events from worker
  • Take eventName and message
• returns a Promise

PromiseWorker.exec(operationName, message, transferableList, onEvent)

Send a message to the worker and return a Promise.

• operationName - string - required
  • Operation name to exec
• message - object
  • The message to send.
• transferable - transferable list
• onEvent - on-event callback function to handle events from worker
  • Take eventName and message
• returns a Promise

Worker bundle

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

registerWebworker(function)

• function
  • Takes a emit fn and message, returns a Promise;

registerWebworker().operation(name, handler)

Add Operation.

• name - string - required
  • The message to send.
• handler - handle the operation

Testing the library

First:

npm install

Then to test in Node using pseudo-webworker

npm test

Or to test with coverage reports:

npm run coverage

Inspired by https://github.com/nolanlawson/promise-worker