jQuery Server Observer Plugin

HTML5's online/offline detection is a good idea but unfortunately it's unusable. Browsers implementations are inconsistent and the specification itself says we can not rely on this attribute.

No matter what online means. As a web developer I only want to know if I can reach the server-side part of my application.

The Server Observer Plugin provides a simple and reliable way to check if the server-side application is available. Hopefully it will help people to use HTML5 offline mode.

Two mechanisms are used to check the server availability:

• By periodically pinging a specified URL
• By observing any and all user-sent Ajax requests.

Thus the client-side application will be notified of any change in the server availability.

Usage

The plugin provides three operations:

• jQuery.serverObserver.enable(options) - Starts observing the server availability.

  The options parameter is a set of key/value pairs that configure the Server Observer:

  • url - Optional - An URL which will be pinged to check the server availability. If no URL is provided, only user-sent Ajax requests will be observed.
  • frequency - Optional, default: 3000 - Time between each ping (in milliseconds).
  • method - Optional, default: HEAD - Type of the ping request.
  • onServerOnline - Function to be called when the server becomes available.
  • onServerOffline - Function to be called when the server becomes unavailable.

• jQuery.serverObserver.disable() - Stops the observation.

• jQuery.serverObserver.isServerOnline() - Returns true if the server's last known status is online.

Example

$.serverObserver.enable({
    url: "ping",
    frequency: 5000,
    onServerOnline: function() {
        // The server is available
    },
    onServerOffline: function() {
        // The server is unavailable
    }
});

Cache

Be sure to tell browsers to not cache the ping URL's response by providing the correct headers. If using the HTML5 Application Cache, make sure that the URL used for pinging your application is declared in the NETWORK section.

Requirements

jQuery Server Observer Plugin can be used with jQuery 1.7 and above.

Todo list

• Write neat tests

Contributing

The Server Observer source code is hosted on GitHub. Please feel free to report issues and submit pull requests.

Changelog

0.9.0 - February 4th, 2013 - a.k.a. 1.0.0 release candidate

• Added the ability to specify the ping request type (default: HEAD)

0.2.0 - August 15th, 2012

• Added the isServerOnline method

0.1.0 - May 10th, 2012

• Initial release

License

jQuery Server Observer Plugin is released under the MIT license (see included LICENSE file).