jquery.ajax-localstorage-cache.js

// github.com/paulirish/jquery-ajax-localstorage-cache
// dependent on Modernizr's localStorage test

$.ajaxPrefilter( function( options, originalOptions, jqXHR ) {
	// Cache it ?
	if ( !Modernizr.localstorage || !options.localCache ) return;

	var hourstl = options.cacheTTL || 5;

	var cacheKey = options.cacheKey || options.url.replace( /jQuery.*/,'' ) + options.type + options.data;
	

	// isCacheValid is a function to validate cache
	if ( options.isCacheValid &&  ! options.isCacheValid() ){
		localStorage.removeItem( cacheKey );
	}
	// if there's a TTL that's expired, flush this item
	var ttl = localStorage.getItem(cacheKey + 'cachettl');
	if ( ttl && ttl < +new Date() ){
		localStorage.removeItem( cacheKey );
		localStorage.removeItem( cacheKey  + 'cachettl' );
		ttl = 'expired';
	}
	
	var value = localStorage.getItem( cacheKey );
	if ( value ) {
		//In the cache? So get it, apply done callback & abort the XHR request
		// parse back to JSON if we can.
		if ( options.dataType.indexOf( 'json' ) === 0 ) value = JSON.parse( value );
		
		//Run the done() callback with our custom value as data, somehow...

		// Abort is broken on JQ 1.5 :(
		jqXHR.abort();
	} else {
		$.Deferred(function(defer) {
			//If it not in the cache, we change the done callback, just put data on localstorage and after that apply the initial callback
			if ( jqXHR.done ) {
				jqXHR.realdone = jqXHR.done;
			}

			jqXHR.done(function(data) {
				var strdata = data;
				if ( options.dataType.indexOf( 'json' ) === 0 ) strdata = JSON.stringify( data );

				// Save the data to localStorage catching exceptions (possibly QUOTA_EXCEEDED_ERR)
				try {
					localStorage.setItem( cacheKey, strdata );
					// store timestamp
					if ( ! ttl || ttl === 'expired' ) {
						localStorage.setItem( cacheKey  + 'cachettl', +new Date() + 1000 * 60 * 60 * hourstl );
					}
				} catch (e) {
					// Remove any incomplete data that may have been saved before the exception was caught
					localStorage.removeItem( cacheKey );
					localStorage.removeItem( cacheKey + 'cachettl' );
					if ( options.cacheError ) options.cacheError( e, cacheKey, strdata );
				}

				if ( jqXHR.realdone ) jqXHR.realdone( defer.resolve );
			}).fail(defer.reject)
		}).promise(jqXHR);
	}
});