msgr

Nifty service worker/client message utility

Made with ❤ at @outlandish

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

• Send messages from client to worker and vice-versa
• Accommodates complex communications with a simple API
• Easily respond to any message
• Receive one-off responses to messages

To see it being used in the wild, check out the source code of fetch-sync.

Table of Contents

• Import
• Initialise & Example
• Sending Messages
• Receiving Messages
• msgr API
• Channel API
• Message API

Import

Client

// 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>

Worker

If you are bundling your SW then you can use the Import methods above.

Otherwise...

// importScripts
importScripts('/node_modules/msgr/index.js')

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: (url, respond) => {
    cache(url).then(function () {
      respond('Caching complete!')
    })
  }
})

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!')

Sending Messages

• Anonymous, data-only message:

  channel.send({ requestId: '123' })

• Type-only message:

  channel.send('RE_CACHE')

• Typed message with data:

  channel.send('RE_CACHE', { assetUrl: '/cat.gif' })

Receiving Messages

The API for receiving messages is the same for both the worker and client.

• Anonymous, data-only message:

  channel.receive((data) => {
    console.log(data.requestId) //=> '123'
  })

• Type-only message:

  msgr.client({
    RE_CACHE: (data, respond) => {
      console.log(data) //=> null
    }
  })

• Typed message with data:

  msgr.client({
    RE_CACHE: (data, respond) => {
      console.log(data.assetUrl) //=> '/cat.gif'
    }
  })

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.