Fetch Sync

A handy wrapper for the Background Sync API

Made with ❤ at @outlandish

Fetch Sync allows you to proxy fetch requests through the Background Sync API so that they are honoured if made when the UA is offline! Hooray!

Check out a live demo here.

If the browser does not support Background Sync, the library will fall back on normal fetch requests.

Note: this is not production ready. Please see the refactor branch for an ongoing overhaul of the library that is a much cleaner implementation (two files, half the LOC).

Install

npm install fetch-sync --save

Table of Contents

• Requirements
• Support
• Features
• Initialisation
• Usage
• Sync API
• Dependencies
• Todo
• Test
• Development
• Contributing
• Author & License

Requirements

The library utilises some new technologies so currently only works in some browsers. It definitely works in Chrome Canary with the experimental-web-platform-features flag enabled.

The browser must support:

• Background Sync
• Service Worker
• Fetch
• IndexedDB
• [Promise] (https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise)

Support

Chrome Canary	Chrome	Firefox	IE	Opera	Safari
✔	✔	✘	✘	✘	✘

Features

• Register a Background Sync operation with one call to fetchSync().

• Uses a fetch-like API. Accepts a Request or String URL, and returns the Promise of a Response.

• Manage sync operations with fetchSync.{get,getAll,cancel,cancelAll}().

• Named sync operations and have their response stored within an IndexedDB store and are synced between client and worker.

• Can be used with existing Service Worker infrastructures with importScripts, or can handle SW registration for you.

Initialise

Existing Service Worker

If your application already uses a Service Worker, you can import the Fetch Sync worker using importScripts:

importScripts('node_modules/fetch-sync/dist/fetch-sync.sw.min.js')

And then call fetchSync.init() somewhere in your application's initialisation procedure.

No Service Worker

Fetch Sync can handle registration if you don't use a SW already...

Either serve the Fetch Sync worker file with a header "Service-Worker-Allowed : /", or to avoid configuring headers, create a Service Worker script in the root of your project and use the method above for 'Existing Service Worker'.

Then see the example under Usage for the fetchSync.init() method.

Usage

fetchSync.init([options]) : Promise

Initialise fetchSync.

• options {Object} (optional) options object

    options {
      // The URL of the fetchSync worker script.
      workerUrl {String} (required, default: null)
  
      // The options object to pass to the worker registration function.
      workerOptions {Object} (optional, default: null)
  
      // Force the worker registration to update the worker script.
      forceUpdate {Boolean} (optional, default: false)
    }
  

Example:

// Import client lib...

// ES6
import fetchSync from 'fetch-sync'

// ES5
var fetchSync = require('fetch-sync')

// Script, using bundled dist
<script src="/node_modules/fetch-sync/dist/fetch-sync.min.js"></script>

// Initialise, passing in worker lib location...

fetchSync.init({
  workerUrl: 'node_modules/fetch-sync/dist/fetch-sync.sw.js',
  workerOptions: {
    scope: '<website address>' // e.g. 'http://localhost:8000'
  }
})

fetchSync([name, ]request[, options]) : Promise<Response>

Perform a sync Background Sync operation.

• [name] {String} (optional) name of the sync operation
• request {String|Request} URL or an instance of fetch Request
• [options] {Object} (optional) fetch options object

Returns a Promise that resolves on success of the fetch request.

If called with a name:

• the response will be stored and can be retrieved later using fetchSync.get(<name>) and then sync.getResponse().
• the response will not automatically be removed from the IDBStore in the worker. You should request that a named sync be removed manually by using sync.remove().
• see the Sync API for more details.

Examples:

• named GET

    fetchSync('GetMessages', '/messages')
      .then((response) => response.json())
      .then((json) => console.log(json.foo))
  

• unnamed POST

    const post = fetchSync('/update-profile', {
      method: 'POST',
      body: { name: '' }
    })
    
    // cancel the sync...
    post.cancel()
  

• unnamed with options

    const headers = new Headers();
    
    headers.append('Authorization', 'Basic abcdefghijklmnopqrstuvwxyz');
    
    // `fetchSync` accepts the same args as `fetch`...
    fetchSync('/send-message', { headers })
  

• named with options

    fetchSync('/get-messages', { headers })
  

• unnamed with Request

    fetchSync(
      new Request('/messages')
    )
  

fetchSync.get(name) : Promise

Get a sync by its name.

• name {String} name of the sync operation to get

Returns the Promise that resolves with success of the sync operation.

There are some properties/methods on the returned Promise. See the Sync API for more details.

Example:

fetchSync('SendMessage', '/message', { body: 'Hello, World!' })
    
const sync = fetchSync.get('SendMessage')
    
sync.then((response) => {
  if (response.ok) {
    alert(`Your message was sent at ${new Date(sync.syncedOn).toDateString()}.`
  } else {
    alert('Message failed to send.')
  }
})

fetchSync.getAll() : Array<Promise>

Get all sync operations.

Returns an array of all sync operations (named and unnamed).

Example:

fetchSync
  .getAll()
  .forEach((sync) => sync.cancel())

fetchSync.cancel(name) : Promise

Cancel the sync with the given name.

• name {String} name of the sync operation to cancel

Example:

fetchSync('Update', '/update', { body })
fetchSync.cancel('Update')

fetchSync.cancelAll() : Promise

Cancel all syncs, named and unnamed.

Sync API

sync.cancel() : Promise

Cancels the sync operation.

Returns a Promise of success of the cancellation.

Example:

const sync = fetchSync.get('Update')
sync.cancel()

sync.getResponse() : Response

Response retrieved when the operation was completed. Or null if the operation is incomplete.

const sync = fetchSync.get('Update')
const response = sync.getResponse()
console.log(response ? response.ok ? 'Response OK' : 'Response not OK' : 'No response')

sync.id

The unique ID of the sync operation. This will be its name if it has one.

sync.name

The name of the sync operation if it has one.

sync.createdOn

The time that the sync operation was created.

sync.syncedOn

The time that the sync operation was completed.

Useful for named syncs that you want to retrieve later on.

Dependencies

• redux (& redux-thunk)
• idb-wrapper
• serialise-request
• serialise-response
• mini-defer

Todo

• Reduce size of client and SW bundles.
• Reduce complexity of lib. (See refactor branch for overhaul.)
• Create more sophisticated gh-pages demo that consumes most of available API.

Test

As the library depends on Service Workers and no headless browser has (good enough) support for Service Workers that would allow tests to be executed within the console, tests are ran through the browser using Mocha and Chai.

On running npm test an Express server will be started at localhost:8000.

Run the tests:

$ cd fetch-sync
$ npm test

Development

The library is bundled by Webpack and transpiled by Babel.

• Install dependencies: npm install
• Start Webpack in a console: npm run watch
• Start the test server in another: npm test
• Navigate to http://localhost:8000

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

fetch-sync was created by Sam Gluck and is released under the MIT license.