# Yahoo! UI Library

### cache 3.0.0b1

Yahoo! UI Library > cache > cache.js (source view)
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    /**
     * The Cache utility provides a common configurable interface for components to
     * cache and retrieve data from a local JavaScript struct.
     *
     * @module cache
     */
    var LANG = Y.Lang,

    /**
     * Base class for the YUI Cache utility.
     * @class Cache
     * @extends Plugin.Base
     * @constructor
     */
    Cache = function() {
        Cache.superclass.constructor.apply(this, arguments);
    };

        /////////////////////////////////////////////////////////////////////////////
        //
        // Cache static properties
        //
        /////////////////////////////////////////////////////////////////////////////
    Y.mix(Cache, {
        /**
         * The namespace for the plugin. This will be the property on the host which
         * references the plugin instance.
         *
         * @property NS
         * @type String
         * @static
         * @final
         * @value "cache"
         */
        NS: "cache",

        /**
         * Class name.
         *
         * @property NAME
         * @type String
         * @static
         * @final
         * @value "cache"
         */
        NAME: "cache",

        ATTRS: {
            /////////////////////////////////////////////////////////////////////////////
            //
            // Cache Attributes
            //
            /////////////////////////////////////////////////////////////////////////////

            /**
            * @attribute max
            * @description Maximum number of entries the Cache can hold.
            * Set to 0 to turn off caching.
            * @type Number
            * @default 0
            */
            max: {
                value: 0,
                validator: function(value) {
                    return (LANG.isNumber(value));
                },
                setter: function(value) {
                    // If the cache is full, make room by removing stalest element (index=0)
                    var entries = this._entries;
                    if(value > 0) {
                        if(entries) {
                            while(entries.length > value) {
                                entries.shift();
                            }
                        }
                    }
                    else {
                        this._entries = [];
                    }
                    return value;
                }
            },

            /**
            * @attribute size
            * @description Number of entries currently cached.
            * @type Number
            */
            size: {
                readOnly: true,
                getter: function() {
                    return this._entries.length;
                }
            },

            /**
             * @attribute entries
             * @description Cached entries.
             * @type Array
             */
            entries: {
                readOnly: true,
                getter: function() {
                    return this._entries;
                }
            }
        }
    });

    Y.extend(Cache, Y.Plugin.Base, {
        /////////////////////////////////////////////////////////////////////////////
        //
        // Cache private properties
        //
        /////////////////////////////////////////////////////////////////////////////

        /**
         * Array of request/response objects indexed chronologically.
         *
         * @property _entries
         * @type Object[]
         * @private
         */
        _entries: null,

        /////////////////////////////////////////////////////////////////////////////
        //
        // Cache private methods
        //
        /////////////////////////////////////////////////////////////////////////////

        /**
        * @method initializer
        * @description Internal init() handler.
        * @param config {Object} Config object.
        * @private
        */
        initializer: function(config) {

            /**
            * @event add
            * @description Fired when an entry is added.
            * @param e {Event.Facade} Event Facade with the following properties:
             * <dl>
             * <dt>entry (Object)</dt> <dd>The cached entry.</dd>
             * </dl>
            * @preventable _defAddFn
            */
            this.publish("add", {defaultFn: this._defAddFn});

            /**
            * @event flush
            * @description Fired when the cache is flushed.
            * @param e {Event.Facade} Event Facade object.
            * @preventable _defFlushFn
            */
            this.publish("flush", {defaultFn: this._defFlushFn});

            /**
            * @event request
            * @description Fired when an entry is requested from the cache.
            * @param e {Event.Facade} Event Facade with the following properties:
            * <dl>
            * <dt>request (Object)</dt> <dd>The request object.</dd>
            * </dl>
            */

            /**
            * @event retrieve
            * @description Fired when an entry is retrieved from the cache.
            * @param e {Event.Facade} Event Facade with the following properties:
            * <dl>
            * <dt>entry (Object)</dt> <dd>The retrieved entry.</dd>
            * </dl>
            */

            // Initialize internal values
            this._entries = [];
            Y.log("Cache initialized", "info", "cache");
        },

        /**
        * @method destructor
        * @description Internal destroy() handler.
        * @private
        */
        destructor: function() {
            this._entries = null;
            Y.log("Cache destroyed", "info", "cache");
        },

        /////////////////////////////////////////////////////////////////////////////
        //
        // Cache protected methods
        //
        /////////////////////////////////////////////////////////////////////////////

        /**
         * Adds entry to cache.
         *
         * @method _defAddFn
         * @param e {Event.Facade} Event Facade with the following properties:
         * <dl>
         * <dt>entry (Object)</dt> <dd>The cached entry.</dd>
         * </dl>
         * @protected
         */
        _defAddFn: function(e) {
            var entries = this._entries,
                max = this.get("max"),
                entry = e.entry;

            // If the cache at or over capacity, make room by removing stalest element (index=0)
            while(entries.length>=max) {
                entries.shift();
            }

            // Add entry to cache in the newest position, at the end of the array
            entries[entries.length] = entry;
            Y.log("Cached entry: " + Y.dump(entry), "info", "cache");
        },

        /**
         * Flushes cache.
         *
         * @method _defFlushFn
         * @param e {Event.Facade} Event Facade object.
         * @protected
         */
        _defFlushFn: function(e) {
            this._entries = [];
            Y.log("Cache flushed", "info", "cache");
        },

        /**
         * Default overridable method compares current request with given cache entry.
         * Returns true if current request matches the cached request, otherwise
         * false. Implementers should override this method to customize the
         * cache-matching algorithm.
         *
         * @method _isMatch
         * @param request {Object} Request object.
         * @param entry {Object} Cached entry.
         * @return {Boolean} True if current request matches given cached request, false otherwise.
         * @protected
         */
        _isMatch: function(request, entry) {
            return (request === entry.request);
        },

        /////////////////////////////////////////////////////////////////////////////
        //
        // Cache public methods
        //
        /////////////////////////////////////////////////////////////////////////////

        /**
         * Adds a new entry to the cache of the format
         * {request:request, response:response, payload:payload}.
         * If cache is full, evicts the stalest entry before adding the new one.
         *
         * @method add
         * @param request {Object} Request value.
         * @param response {Object} Response value.
         * @param payload {Object} (optional) Arbitrary data payload.
         */
        add: function(request, response, payload) {
            if(this.get("entries") && (this.get("max")>0) &&
                    (LANG.isValue(request) || LANG.isNull(request) || LANG.isUndefined(request))) {
                this.fire("add", {entry: {request:request, response:response, payload:payload}});
            }
            else {
                Y.log("Could not add " + Y.dump(response) + " to cache for " + Y.dump(request), "info", "cache");
            }
        },

        /**
         * Flushes cache.
         *
         * @method flush
         */
        flush: function() {
            this.fire("flush");
        },

        /**
         * Retrieves cached entry for given request, if available, and refreshes
         * entry in the cache. Returns null if there is no cache match.
         *
         * @method retrieve
         * @param request {Object} Request object.
         * @return {Object} Cached entry object with the properties request, response, and payload, or null.
         */
        retrieve: function(request) {
            // If cache is enabled...
            var entries = this._entries,
                length = entries.length,
                entry = null,
                i = length-1;

            if((this.get("max") > 0) && (length > 0)) {
                this.fire("request", {request: request});

                // Loop through each cached entry starting from the newest
                for(; i >= 0; i--) {
                    entry = entries[i];

                    // Execute matching function
                    if(this._isMatch(request, entry)) {
                        this.fire("retrieve", {entry: entry});

                        // Refresh the position of the cache hit
                        if(i < length-1) {
                            // Remove element from its original location
                            entries.splice(i,1);
                            // Add as newest
                            entries[entries.length] = entry;
                            Y.log("Refreshed cache entry: " + Y.dump(entry) +
                                    " for request: " +  Y.dump(request), "info", "cache");
                        }

                        Y.log("Retrieved cached response: " + Y.dump(entry) +
                                " for request: " + Y.dump(request), "info", "cache");
                        return entry;
                    }
                }
            }
            return null;
        }
    });

    Y.Cache = Cache;

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