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HTML5's localStorage caching layer for fetching JSON data with jQuery.

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README.rst

JSONCache

JSONCache is a caching layer for fetching JSON data with jQuery. It uses HTML5's window.localStorage to cache fetched JSON data to avoid unnecessary network requests.

The primary goal of the library is to minimize network requests for mobile devices.

See also the project page at http://kpuputti.github.com/JSONCache/

Licence

JSONCache is licenced under the MIT licence. See LICENCE file for more information.

Requirements

  • jQuery (tested with 1.6.2, 1.6.3)
  • JSON.parse and JSON.stringify (available in the latest browsers or e.g. with json2.js available at https://github.com/douglascrockford/JSON-js)
  • window.localStorage (available in the latest browsers)

Usage

  1. Make sure you have all the requirements.
  2. Download the minified jsoncache-{version}.min.js file and include it on your page.
  3. Use the JSONCache.getCachedJSON function instead of jQuery.getJSON to fetch your data.

JSONCache.getCachedJSON attempts to provide the same API as the jQuery.ajax function.

Basic example:

JSONCache.getCachedJSON('http://example.com/data.json', {
    success: function (data) {
        // handle data
    }
});

Example with function hooks to display status info to user:

// Message container to show info to user.
var message = $('#message');

JSONCache.getCachedJSON('http://example.com/data.json', {
    ontry: function (tryNumber) {
        // Called before each fetch attempt.
        console.log('Fetch number:', tryNumber);
    },
    onerror: function (jqXHR, textStatus, errorThrown, tryNumber) {
        // Called when jQuery.ajax fails.
        message.text('Failed fetch number ' + tryNumber + '. Trying again...');
    },
    ongiveup: function (status) {
        // Called when all fetch attemps fail.
        if (status === 'timeout') {
            message.text('Network failure, cannot fetch data.');
        } else {
            message.text('Failed to get data.');
        }
    },
    success: function (data) {
        message.text('Data fetched successfully!');
    }
);

Configuration

Global configuration:

Global configuration options can be set by modifying the JSONCache.options object directly. Available options:

JSONCache.options.debug: (boolean) toggle console debugging

JSONCache.options.numTries: (number) number of times the JSON is attempted to fetch on network errors

JSONCache.options.waitTime: (number) time in milliseconds to wait after a network error before a re-try. Note that this time is doubled after each try.

JSONCache.options.itemLifetime: (number) Cache item validity lifetime in milliseconds.

JSONCache.options.maxCacheSize: (number) Maximum cache size in bytes that JSONCache uses. null for unlimited size.

JSONCache.options.autoEvict: (boolean) Flag to indicate whether old entries should be removed from the cache if the cache fills up.

Function hooks:

Function hooks can be given in the options object in JSONCache.getCachedJSON function call. Available hooks:

success(data): Called with the requested JSON data if it was found in the cache or successfully fetched.

ontry(tryNumber): Called before each network fetch attemp. The try counter is provided as an argument (starting from 1).

onerror(jqXHR, textStatus, errorThrown, tryNumber): Called when a fetch fails. The arguments are forwarded from the jQuery error hook in addition to the try number.

ongiveup(status): Called when all attemps fail or if there is an error with the cache. Possible statuses are timeout when all attemps failed and addfailure when there was a problem when adding data to localStorage.

Testing

JSONCache test suite uses Jasmine ( https://github.com/pivotal/jasmine/wiki ) for its test framework. The tests can be run by typing:

make test # for dev and production
make test_dev # for dev
make test_prop # for production

The command line test runner uses PhantomJS ( http://www.phantomjs.org/ ). The tests can also be run by opening the tests/index.html in a browser and clicking on the jasmine test links.

Old QUnit tests are still available in the same index.html.

TODO

  • Add support for item-specific cache lifetime.
  • Add better support for user defined error handling.
  • Fail more gracefully when JSON object or localStorage are not supported (by bypassing the cache and just forwarding the requests to jQuery).
  • Integrate with window.navigator.onLine if present.
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