Offline

Note to users pre-0.6.0: Offline previously used a cloudfront hosted file as one of it's methods of detecting the connection status. This method is now deprecated. If your app is getting cloudfront 404s, please upgrade to Offline 0.6.0.

Improve the experience of your app when your users lose connection.

• Monitors ajax requests looking for failure
• Confirms the connection status by requesting an image or fake resource
• Automatically grabs ajax requests made while the connection is down and remakes them after the connection is restored.
• Simple UI with beautiful themes
• 3kb minified and compressed

Installing

Include the javascript and one of the themes on your site. You're done!

Advanced

Optionally, you can provide some configuration by setting Offline.options after bringing in the script.

Options (any can be provided as a function), with their defaults:

{
  // Should we check the connection status immediatly on page load.
  checkOnLoad: false,

  // Should we monitor AJAX requests to help decide if we have a connection.
  interceptRequests: true,

  // Should we automatically retest periodically when the connection is down (set to false to disable).
  reconnect: {
    // How many seconds should we wait before rechecking.
    initialDelay: 3,

    // How long should we wait between retries.
    delay: (1.5 * last delay, capped at 1 hour)
  },

  // Should we store and attempt to remake requests which fail while the connection is down.
  requests: true,

  // Should we show a snake game while the connection is down to keep the user entertained?
  // It's not included in the normal build, you should bring in js/snake.js in addition to
  // offline.min.js.
  game: false
}

Properties

Offline.check(): Check the current status of the connection.

Offline.state: The current state of the connection 'up' or 'down'

Offline.on(event, handler, context): Bind an event. Events:

• up: The connection has gone from down to up
• down: The connection has gone from up to down
• confirmed-up: A connection test has succeeded, fired even if the connection was already up
• confirmed-down: A connection test has failed, fired even if the connection was already down
• checking: We are testing the connection
• reconnect:started: We are beginning the reconnect process
• reconnect:stopped: We are done attempting to reconnect
• reconnect:tick: Fired every second during a reconnect attempt, when a check is not happening
• reconnect:connecting: We are reconnecting now
• reconnect:failure: A reconnect check attempt failed
• requests:flush: Any pending requests have been remade
• requests:hold: A new request is being held

Offline.off(event, handler): Unbind an event

Checking

Offline ships with two methods for checking the connection. One makes a request for a tiny image hosted on a cloudfront account for the benevolence of all, the other makes an XHR request against the current domain, hoping to get back any sort of response (even a 404).

You can change the url of the image to be one you control, if you like:

Offline.options = {checks: {image: {url: 'my-image.gif'}}};

Loading an image was chosen (rather than a script file), because it limits the potential damage if a hostile party were to be in control of it.

You can also switch to the XHR method:

Offline.options = {checks: {active: 'xhr'}}

The XHR method is not enabled by default because of a concern that some sites do a significant amount of processing to build their 404 page, so it's not something we want to send unnecessarily. It's also possible that the page would respond with a redirect to a different domain, creating a CORS problem. If you have control of the domain and can create an endpoint which just responds with a quick 204, that's the perfect solution. You can set the endpoint in settings as well:

Offline.options = {checks: {xhr: {url: '/health-check'}}};

Reconnect

The reconnect module automatically retests the connection periodically when it is down. A successful AJAX request will also trigger a silent recheck (if interceptRequests is not false).

You can disable the reconnect module by setting the reconnect to false. Reconnect can be configured by setting options on the reconnect setting.

Requests

The requests module holds any failed AJAX requests and, after deduping them, remakes them when the connection is restored.

You can disable it by setting the requests setting to false.

Dependencies

None!

Browser Support

Modern Chrome, Firefox, Safari and IE8+