fetch-sync

Proxy fetch requests through 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.

• Make requests offline that will be sent when the UA regains connectivity (even if the web page is no longer open).
• Responses are forwarded back to the client as soon as they are received.
• Implements a familiar fetch-like API: similar function signature and the same return type (a Response).
• Make named requests that have their response stored in an IDBStore which you can collect in subsequent user sessions.
• Manage sync operations with

  fetchSync.{get,getAll,cancel,cancelAll}()

  .
• Can be used with existing Service Worker infrastructures with

  importScripts

  , or handles SW registration for you.
• If the browser does not support Background Sync, the library will fall back on normal

  fetch

  requests.

Install

npm install fetch-sync --save

Table of Contents

• Requirements
• Support
• Import
• Initialise
• Usage
• Sync API
• Dependencies
• 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

The browser must support:

• Background Sync
• Service Worker
• Fetch
• IndexedDB
• Promise

Support

Import

Client

// ES6
import fetchSync from 'fetch-sync'

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

Worker

See Initialise for details on importing and registering the service worker.

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()

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 : /"

Then see the example under Usage for the

fetchSync.init()

Usage

fetchSync.init([options]) : Promise

Initialise fetchSync.

• options {Object} (optional) options object

Look at the documentation for

sw-register

Example:

// Import client lib...

// ES6
import fetchSync from 'fetch-sync'
// ES5
var fetchSync = require('fetch-sync')

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

fetchSync.init({
  url: 'node_modules/fetch-sync/dist/fetch-sync.sw.js',
  scope: '' // e.g. 'http://localhost:8000'
})

fetchSync([name, ]request[, options]) : Sync

Perform a

sync

• [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. Rejects if a sync exists with this name already.

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

If called with a

name

• the response will be stored and can be retrieved later using e.g.

  fetchSync.get('name').then(sync => sync.response)

  .
• 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) : Sync

Get a sync by its name.

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

Returns a Promise that resolves with success of the sync operation or reject if sync operation is not found.

There are also some properties/methods on the 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 received at ${new Date(sync.syncedOn).toDateString()}.
  } else {
    alert('Message failed to send.')
  }
})

fetchSync.getAll() : Array

Get all sync operations.

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

Example:

fetchSync.getAll()
  .then((syncs) => syncs.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.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.

Dependencies

• idb-wrapper
• msgr
• sw-register
• serialise-request
• serialise-response
• mini-defer

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

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