msgr

Nifty worker/client postMessage utility

Made with ❤ at @outlandish

Makes communication between a client and service worker super easy...

• Send messages from client -> worker and worker -> client with one call to channel.send()
• Simple API: send anonymous data-only messages, typed-only messages, or typed messages with data
• Register handlers for typed messages and anonymous messages
• Easily respond to any message by calling respond() in the handler
• Receive a response for a message using the familiar Promise then() method

Table of Contents

• Import
• Initialise & Example
• msgr API
• Channel API
• Message API

Import

// ES6
import msgr from 'msgr'

// CommonJS
var msgr = require('msgr')

// RequireJS
define(['msgr'], function (msgr) {/*...*/})

<!-- Script, available as `window.msgr` -->
<script src="/node_modules/msgr/index.js"></script>

Initialise & Example

Client: msgr.client()

Pass in reference to the worker and a collection of message handlers:

const recipient = navigator.serviceWorker.controller

const channel = msgr.client(recipient, {
  // Predefined message handlers
  SAY_HELLO: (data) => console.log('Hello, ' + data) //=> 'Hello, World!'
})

// Send something "unknown" to the worker.
// Notice it does not have a tag.
channel.send({
  username: 'Flanders',
  location: 'Springfield'
})

// Send a "known" message to the worker
channel.send('CACHE_ASSET', '/cat.gif').then(function (message) {
  console.log(message) //=> 'Caching complete!'
})

Worker: msgr.worker()

On the worker you just pass in your message handlers:

const channel = msgr.worker({
  CACHE_ASSET: cacheAsset
})

channel.receive(function (data) {
  // Do something with an "unknown" message
  // that does not have a predefined handler.
  console.log(data) //=> { username: 'Flanders', ... }
})

// Send something "known" to the client using a tag.
channel.send('SAY_HELLO', 'World!')

function cacheAsset (url, respond) {
  doCaching().then(function () {
    respond('Caching complete!')
  })
}

msgr API

msgr.client(serviceWorker, handlers) : Channel

Initialise a msgr client.

• serviceWorker {ServiceWorkerRegistration} Worker that will receive messages sent via channel
• handlers {Object} An object of message type/handler mappings

Returns a Channel. See the Channel API Docs for more details.

Example:

msgr.client(navigator.serviceWorker.controller, {
  NOTIFY: function (respond) {
    new Notification('You have a notification!')
    respond('GOT_THE_NOTIFICATION')
  }
})

msgr.worker(handlers) : Channel

Initialise a msgr worker.

• handlers {Object} An object of message type/handler mappings

Returns a Channel. See the Channel API Docs for more details.

Example:

msgr.worker({
  NOTIFY: function (respond) {
    new Notification('You have a notification!')
    respond('GOT_THE_NOTIFICATION')
  }
})

Channel API

channel.ready(handler)

Register a handler to be called when the channel is opened between client and worker.

• handler {Function} The ready handler

Although you can register ready handlers, you can send messages before the channel is open using channel.send() and these will be queued and sent as soon as the channel is ready.

Example:

channel.ready(function () {
  application.start()
})

channel.send([type,] data) : Promise

Send a message through the channel to the worker/client.

• [type] {String} (optional) The message type
• data {Any} The message data (it will be JSON.stringify'd)

Returns a Message. See the Message API Docs for more details.

If called before the channel is ready the message will be queued and sent as soon as the channel is open.

Example:

// Typed message, will invoke registered type handlers
channel.send('NOTIFY_USER')

// Typed message with data, will invoke registered type handlers
channel.send('NOTIFY_USER', { message: 'Update complete' })

// Anonymous, will invoke `receive` handlers
channel.send('This is the untagged data')

channel.receive(handler)

Handle an "unknown" message that is not tagged.

• handler {Function} The message handler

The handler receives two arguments: the data of the message and a respond function.

Example:

channel.receive(function (data, respond) {
  console.log('Got some unknown data: ' + data)
})

Message API

message.then(handler)

Register a handler to receive the response to a message.

• handler {Function} Response handler

Example:

// In client message handlers
msgr({
  NOTIFY_USER: function (data, respond) {
    new Notification('Job ' + data.id + ' was completed')
    respond('From worker: job deleted') // ACK
  }
})

// In worker
channel.send('NOTIFY_USER', { id: 1337 }).then((data) => {
  console.log(data) //=> 'From worker: job deleted'
})

respond([data])

Send a response to a received message.

This function is passed as the second argument to both "known" and "unknown" message handlers.

• [data] {Any} (optional) The data to respond to the message with

Contributing

All pull requests and issues welcome!

If you're not sure how, check out Kent C. Dodds' great video tutorials on egghead.io!

Author & License

msgr was created by Sam Gluck and is released under the MIT license.