API: Storage Storage.js (YUI Library)

# Yahoo! UI Library

### Storage 2.8.1

Yahoo! UI Library > Storage > Storage.js (source view)
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    /**
     * The Storage module manages client-side data storage.
     * @module Storage
     */

    (function() {

    	// internal shorthand
    var Y = YAHOO,
    	YU = Y.util,
    	YL = Y.lang,
    	_logOverwriteError;

    if (! YU.Storage) {
    	_logOverwriteError = function(fxName) {
    		Y.log('Exception in YAHOO.util.Storage.?? - must be extended by a storage engine'.replace('??', fxName).replace('??', this.getName ? this.getName() : 'Unknown'), 'error');
    	};

    	/**
    	 * The Storage class is an HTML 5 storage API clone, used to wrap individual storage implementations with a common API.
    	 * @class Storage
    	 * @namespace YAHOO.util
    	 * @constructor
    	 * @param location {String} Required. The storage location.
    	 * @parm name {String} Required. The engine name.
    	 * @param conf {Object} Required. A configuration object.
    	 */
    	YU.Storage = function(location, name, conf) {
    		var that = this;
    		Y.env._id_counter += 1;

    		// protected variables
    		that._cfg = YL.isObject(conf) ? conf : {};
    		that._location = location;
    		that._name = name;
    		that.isReady = false;

    		// public variables
    		that.createEvent(that.CE_READY, {scope: that});
    		that.createEvent(that.CE_CHANGE, {scope: that});

    		that.subscribe(that.CE_READY, function() {
    			that.isReady = true;
    		});
    	};

    	YU.Storage.prototype = {

    		/**
    		 * The event name for when the storage item is ready.
    		 * @property CE_READY
    		 * @type {String}
    		 * @public
    		 */
    		CE_READY: 'YUIStorageReady',

    		/**
    		 * The event name for when the storage item has changed.
    		 * @property CE_CHANGE
    		 * @type {String}
    		 * @public
    		 */
    		CE_CHANGE: 'YUIStorageChange',

    		/**
    		 * The delimiter uesed between the data type and the data.
    		 * @property DELIMITER
    		 * @type {String}
    		 * @public
    		 */
    		DELIMITER: '__',

    		/**
    		 * The configuration of the engine.
    		 * @property _cfg
    		 * @type {Object}
    		 * @protected
    		 */
    		_cfg: '',

    		/**
    		 * The name of this engine.
    		 * @property _name
    		 * @type {String}
    		 * @protected
    		 */
    		_name: '',

    		/**
    		 * The location for this instance.
    		 * @property _location
    		 * @type {String}
    		 * @protected
    		 */
    		_location: '',

    		/**
    		 * The current length of the keys.
    		 * @property length
    		 * @type {Number}
    		 * @public
    		 */
    		length: 0,

    		/**
    		 * This engine singleton has been initialized already.
    		 * @property isReady
    		 * @type {String}
    		 * @protected
    		 */
    		isReady: false,

    		/**
    		 * Clears any existing key/value pairs.
    		 * @method clear
    		 * @public
    		 */
    		clear: function() {
    			this._clear();
    			this.length = 0;
    		},

    		/**
    		 * Fetches the data stored and the provided key.
    		 * @method getItem
    		 * @param key {String} Required. The key used to reference this value (DOMString in HTML 5 spec).
    		 * @return {String|NULL} The value stored at the provided key (DOMString in HTML 5 spec).
    		 * @public
    		 */
    		getItem: function(key) {
    			Y.log("Fetching item at  " + key);
    			var item = this._getItem(key);
    			return YL.isValue(item) ? this._getValue(item) : null; // required by HTML 5 spec
    		},

    		/**
    		 * Fetches the storage object's name; should be overwritten by storage engine.
    		 * @method getName
    		 * @return {String} The name of the data storage object.
    		 * @public
    		 */
    		getName: function() {return this._name;},

    		/**
    		 * Tests if the key has been set (not in HTML 5 spec); should be overwritten by storage engine.
    		 * @method hasKey
    		 * @param key {String} Required. The key to search for.
    		 * @return {Boolean} True when key has been set.
    		 * @public
    		 */
    		hasKey: function(key) {
    			return YL.isString(key) && this._hasKey(key);
    		},

    		/**
    		 * Retrieve the key stored at the provided index; should be overwritten by storage engine.
    		 * @method key
    		 * @param index {Number} Required. The index to retrieve (unsigned long in HTML 5 spec).
    		 * @return {String} Required. The key at the provided index (DOMString in HTML 5 spec).
    		 * @public
    		 */
    		key: function(index) {
    			Y.log("Fetching key at " + index);

    			if (YL.isNumber(index) && -1 < index && this.length > index) {
    				var value = this._key(index);
    				if (value) {return value;}
    			}

    			// this is thrown according to the HTML5 spec
    			throw('INDEX_SIZE_ERR - Storage.setItem - The provided index (' + index + ') is not available');
    		},

    		/**
    		 * Remove an item from the data storage.
    		 * @method setItem
    		 * @param key {String} Required. The key to remove (DOMString in HTML 5 spec).
    		 * @public
    		 */
    		removeItem: function(key) {
    			Y.log("removing " + key);

    			if (this.hasKey(key)) {
                    var oldValue = this._getItem(key);
                    if (! oldValue) {oldValue = null;}
                    this._removeItem(key);
    				this.fireEvent(this.CE_CHANGE, new YU.StorageEvent(this, key, oldValue, null, YU.StorageEvent.TYPE_REMOVE_ITEM));
    			}
    			else {
    				// HTML 5 spec says to do nothing
    			}
    		},

    		/**
    		 * Adds an item to the data storage.
    		 * @method setItem
    		 * @param key {String} Required. The key used to reference this value (DOMString in HTML 5 spec).
    		 * @param data {Object} Required. The data to store at key (DOMString in HTML 5 spec).
    		 * @public
    		 * @throws QUOTA_EXCEEDED_ERROR
    		 */
    		setItem: function(key, data) {
    			Y.log("SETTING " + data + " to " + key);

    			if (YL.isString(key)) {
    				var eventType = this.hasKey(key) ? YU.StorageEvent.TYPE_UPDATE_ITEM : YU.StorageEvent.TYPE_ADD_ITEM,
    					oldValue = this._getItem(key);
    				if (! oldValue) {oldValue = null;}

    				if (this._setItem(key, this._createValue(data))) {
    					this.fireEvent(this.CE_CHANGE, new YU.StorageEvent(this, key, oldValue, data, eventType));
    				}
    				else {
    					// this is thrown according to the HTML5 spec
    					throw('QUOTA_EXCEEDED_ERROR - Storage.setItem - The choosen storage method (' +
    						  this.getName() + ') has exceeded capacity');
    				}
    			}
    			else {
    				// HTML 5 spec says to do nothing
    			}
    		},

    		/**
    		 * Implementation of the clear login; should be overwritten by storage engine.
    		 * @method _clear
    		 * @protected
    		 */
    		_clear: function() {
    			_logOverwriteError('_clear');
    			return '';
    		},

    		/**
    		 * Converts the object into a string, with meta data (type), so it can be restored later.
    		 * @method _createValue
    		 * @param s {Object} Required. An object to store.
    		 * @protected
    		 */
    		_createValue: function(s) {
    			var type = (YL.isNull(s) || YL.isUndefined(s)) ? ('' + s) : typeof s;
    			return 'string' === type ? s : type + this.DELIMITER + s;
    		},

    		/**
    		 * Implementation of the getItem login; should be overwritten by storage engine.
    		 * @method _getItem
    		 * @param key {String} Required. The key used to reference this value.
    		 * @return {String|NULL} The value stored at the provided key.
    		 * @protected
    		 */
    		_getItem: function(key) {
    			_logOverwriteError('_getItem');
    			return '';
    		},

    		/**
    		 * Converts the stored value into its appropriate type.
    		 * @method _getValue
    		 * @param s {String} Required. The stored value.
    		 * @protected
    		 */
    		_getValue: function(s) {
    			var a = s ? s.split(this.DELIMITER) : [];
    			if (1 == a.length) {return s;}

    			switch (a[0]) {
    				case 'boolean': return 'true' === a[1];
    				case 'number': return parseFloat(a[1]);
    				case 'null': return null;
    				default: return a[1];
    			}
    		},

    		/**
    		 * Implementation of the key logic; should be overwritten by storage engine.
    		 * @method _key
    		 * @param index {Number} Required. The index to retrieve (unsigned long in HTML 5 spec).
    		 * @return {String|NULL} Required. The key at the provided index (DOMString in HTML 5 spec).
    		 * @protected
    		 */
    		_key: function(index) {
    			_logOverwriteError('_key');
    			return '';
    		},

    		/*
    		 * Implementation to fetch evaluate the existence of a key.
    		 * @see YAHOO.util.Storage._hasKey
    		 */
    		_hasKey: function(key) {
    			return null !== this._getItem(key);
    		},

    		/**
    		 * Implementation of the removeItem login; should be overwritten by storage engine.
    		 * @method _removeItem
    		 * @param key {String} Required. The key to remove.
    		 * @protected
    		 */
    		_removeItem: function(key) {
    			_logOverwriteError('_removeItem');
    			return '';
    		},

    		/**
    		 * Implementation of the setItem login; should be overwritten by storage engine.
    		 * @method _setItem
    		 * @param key {String} Required. The key used to reference this value.
    		 * @param data {Object} Required. The data to storage at key.
    		 * @return {Boolean} True when successful, false when size QUOTA exceeded.
    		 * @protected
    		 */
    		_setItem: function(key, data) {
    			_logOverwriteError('_setItem');
    			return '';
    		}
    	};

    	YL.augmentProto(YU.Storage, YU.EventProvider);
    }

    }());

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