ssw.js

/*
 * Session Storage Wrapper - Cross Document Transport of JavaScript Data
 *
 * Extensible Wrapper for HTML 5's DOM Storage, Microsoft's UserData,
 * Session Cookies and window.name using JSON serialization
 *
 * Author: Mathias Schaefer <molily@mailbox.org>
 * License: Public Domain
 *
 */

/* Anonymous Function Wrapper to establish a local variable scope */

(function (window, document) {

	/* ******************************************************************** */
	/* Public Interface Name */

	var publicInterfaceName = "ssw";

	/* ******************************************************************** */
	/* Helper Functions */

	var helper = {

		/*
		 * Iteration of objects and arrays
		 * Fire the callback function for each member and break if it returns a value.
		 * In this case, pass this return value on.
		 * The callback gets the member as first parameter, the index or name as second.
		 * In the callback, "this" points to the object or array.
		 */

		forEach : function (obj, func) {
			if (obj.constructor == Array) {
				// Array (defined order)
				for (var i = 0, length = obj.length; i < length; i++) {
					var result = func.call(obj, obj[i], i);
					if (result != undefined) {
						return result;
					}
				}
			} else {
				// Object (order not relevant)
				for (var name in obj) {
					if (obj.hasOwnProperty(name)) {
						var result = func.call(obj, obj[name], name);
						if (result != undefined) {
				  			return result;
				  		}
					}
				}
			}
			return null;
		},

		/*
		 * Copy all members of one object to another object
		 * (objects are referenced, primitives are copied)
		 */

		mixin : function (source, target) {
			helper.forEach(source, function (value, name) {
				target[name] = value;
			});
			return target;
		},

		/*
		 * Bind a function to an object so the "this" keyword points to the given object
		 */

		bind : function (func, obj) {
			return function () {
				return func.apply(obj, arguments);
			};
		},

		/*
		 * Load an external JavaScript
		 */

		loadScript : function (uri) {
			/* Load and evaluate the script with synchronous XMLHttpRequest.
			That's really ugly, but there's no other reliable solution.
			Otherwise it cannot be guaranteed that the dependancy is fully loaded
			and executed by the time the public methods of this script are used. */
			/* TODO: Switch to an asynchronous API */
			var req = (window.XMLHttpRequest ? new XMLHttpRequest : (window.ActiveXObject ? new ActiveXObject('Microsoft.XMLHTTP') : false));
			if (!req) {
				return false;
			}
			req.open('GET', uri, false);
			req.send(null);
			eval(req.responseText);
		}
	};


	/* ******************************************************************** */
	/* Serializers */

	var serializers = {

		/* JSON Serializer */

		json : {

			/* URI of the JSON script */

			scriptUri : "./json2.js",

			init : function () {
				/* Load additional script if there's no native JSON implementation */
				if (!window.JSON) {
					helper.loadScript(this.scriptUri);
				}
			},

			serialize : function (object) {
				if (!(window.JSON && JSON.stringify)) {
					throw new Error("JSON serialization not available");
				}
				return JSON.stringify(object);
			},

			unserialize : function (string) {
				if (!(window.JSON || JSON.parse)) {
					throw new Error("JSON parsing not available");
				}
				return JSON.parse(string);
			}

		}

	};

	/* ******************************************************************** */
	/* Implementation Object */

	var implementation = {

		/* Implementation List (an array and a hash at the same time) */

		list: [],

		/* Add an implementation (with possibility to mixin a template) */

		add : function (obj1, obj2) {
			/* Prepare implementation object, mixin template if two objects are given */
			var imp = arguments.length == 1 ? obj1 : helper.mixin(obj1, obj2);
			if (imp) {
				/*
				 * Push the object into the array *and* save it as a property
				 * so we can retrieve it by index or name.
				 */
				this.list.push(imp);
				this.list[imp.name] = imp;
			}
		},

		/* Get an implementation object by index or name */

		get : function (param) {
			return this.list[param];
		},

		/* Auto-Detect available implementation */

		detect : function () {
			/* Iterate over implementation list, check if the implementation is available,
			set the available property accordingly and make use of the first supported implementation */
			var availableImp = null;
			helper.forEach(this.list, function (imp) {
				if (imp.isAvailable()) {
					imp.available = true;
					availableImp = availableImp || imp;
				} else {
					imp.available = false;
				}
			});
			this.setup(availableImp);
		},

		/* Force an implementation (override auto-detect, but check availability) */

		force : function (name) {
			var imp = this.get(name);
			if (!imp || !imp.available) {
				imp = false;
			}
			return this.setup(imp);
		},

		/* Setup and initialize an implementation */

		setup : function (imp) {
			/* If the implementation is not supported, set the global object to false and break */
			if (!imp) {
				return window[publicInterfaceName] = false;
			 }

			/* Call the specific init function of the implementation */
			imp.init();

			/* Set up the public interface object */
			var publicInterface = {
				/* Provide chosen implementation */
				implementation : imp,
				/* Provide method to force another implementation */
				forceImplementation : helper.bind(this.force, this)
			};

			/* Provide core methods from the implementation */
			helper.forEach(["get", "add", "remove", "clear"], function (methodName) {
				/* Copy the bound function to the public interface */
				publicInterface[methodName] = helper.bind(imp[methodName], imp);
			});

			/* Finally, create the global object */
			return window[publicInterfaceName] = publicInterface;
		}

	};

	/* ******************************************************************** */
	/* Implementation Templates (Mixins) */

	var mixins = {

		/* Template for implementations which save all data in a serialized string */

		serialized: {

			/* Private members */

			/* Use JSON as standard serializer */

			serializer: serializers.json,

			/* Store Object */

			box: null,

			/* Initialization */

			init : function () {
				/* Initialize serializer. */
				this.serializer.init();

				/* Call the specific init method */
				if (this.specificInit) {
					this.specificInit();
				}
			},

			/*
			 * Implementation specific private methods:
			 * 	isAvailable
			 * 	read
			 * 	save
			 * 	specificInit   (optional)
			 * 	specificClear   (optional)
			 */

			/* Internal members */

			readBox : function () {
				/* Initial reading and unserializing if box hasn't been set up */
				if (this.box) {
					return;
				}
				var string = this.read();
				this.box = string && string.charAt(0) == "{" ? this.serializer.unserialize(string) : {};
			},

			saveBox : function () {
				var serializedString = this.serializer.serialize(this.box);
				this.save(serializedString);
			},

			/* Public members */

			get : function (param1) {
				this.readBox();
				return param1 != undefined ? this.box[param1] : this.box;
			},

			add : function (param1, value) {
				this.readBox();
				if (arguments.length == 1) {
					helper.mixin(param1, this.box);
				} else {
					this.box[param1] = value;
				}
				this.saveBox();
			},

			remove : function (name) {
				this.readBox();
				if (name in this.box) {
					delete this.box[name];
					this.saveBox();
				}
			},

			clear : function () {
				this.box = {};
				this.saveBox();
				if (this.specificClear) {
					this.specificClear();
				}
			}

		}
	};

	/* ******************************************************************** */
	/* Implementations */

	/* -------------------------------------------------------------------- */
	/* DOM Storage, using serialized template */

	implementation.add(mixins.serialized, {

		name: "domstorage",

		/* Necessary methods */

		isAvailable : function () {
			return Boolean(window.sessionStorage);
		},

		read : function () {
			var serializedString = sessionStorage.getItem(this.storeName);
			return serializedString === null ? "" : serializedString.toString();
		},

		save : function (serializedString) {
			return sessionStorage.setItem(this.storeName, serializedString);
		},

		/* Internal members */

		storeName : publicInterfaceName,

		specificInit : function () {
		},

		specificClear : function () {
		}

	});

	/* -------------------------------------------------------------------- */
	/* userData, using serialized template */

	implementation.add(mixins.serialized, {

		name : "userdata",

		/* Necessary methods */

		isAvailable : function () {
			return Boolean(document.documentElement && document.documentElement.addBehavior);
		},

		read : function () {
			this.element.load(this.storeName);
			return this.element.getAttribute(this.storeName);
		},

		save : function (serializedString) {
			this.element.setAttribute(this.storeName, serializedString);
			this.element.save(this.storeName);
		},

		/* Internal members */

		/* Fictional tag name of the element which gets the userData behavior */
		storeName : publicInterfaceName,

		specificInit : function () {
			/* Create a non-existing element and append it to the root element (html) */
			var el = document.createElement(this.storeName);
			document.documentElement.appendChild(el);
			/* Apply userData behavior */
			el.addBehavior("#default#userData");
			this.element = el;
		},

		specificClear : function () {
			/* Expire at once */
			this.element.expires = new Date(0).toUTCString();
		}

	});

	/* -------------------------------------------------------------------- */
	/* Cookie, using serialized template */

	implementation.add(mixins.serialized, {

		name : "cookie",

		/* Necessary methods */

		isAvailable : function () {
			/* Try to set and get a cookie to test if session cookies are allowed */
			var s = this.cookieName + "-test";
			this.setCookie(s, s);
			return this.getCookie(s) == s ? (this.deleteCookie(s), true) : false;
		},

		read : function () {
			return this.getCookie(this.cookieName);
		},

		save : function (serializedString) {
			if (!serializedString) {
				/* break if the string is empty */
				return;
			}
			this.setCookie(this.cookieName, serializedString);
		},

		/* Internal members */

		cookieName : publicInterfaceName,

		specificClear : function () {
			this.deleteCookie(this.cookieName);
		},

		escapeCookie : function (value) {
			/*
			 * Just escape semicolon and double quotes (the latter escpecially for Opera),
			 * which is more economic than using encodeURIComponent/decodeURIComponent.
			 */
			return value.replace(/%/g, "%%").replace(/;/g, "%S").replace(/"/g, '%Q');
		},

		unescapeCookie : function (value) {
			return value.replace(/%Q/g, '"').replace(/%S/g, ";").replace(/%%/g, "%");
		},

		getCookie : function (name) {
			var pairs = document.cookie.split(/;\s*/),
				value = helper.forEach(pairs, function (str) {
					if (!str) {
						return;
					}
					var separatorPosition = str.indexOf("="),
						testName = str.substring(0, separatorPosition);
					if (testName == name) {
						return str.substring(separatorPosition + 1);
					}
				});
			if (!value) {
				return false;
			}
			return this.unescapeCookie(value);
		},

		setCookie : function (name, value) {
			var cookieString = name + "=" + this.escapeCookie(value);
			if (cookieString.length > 4096) {
				throw new Error("Cookie size exceeds 4096 byte limit");
			}
			document.cookie = cookieString;
		},

		deleteCookie : function (name) {
			document.cookie = name + '=;expires=' + new Date(0).toUTCString();
		}

	});

	/* -------------------------------------------------------------------- */
	/* Window name, using serialized template */

	implementation.add(mixins.serialized, {

		name: "windowname",

		/* Necessary methods */

		isAvailable : function () {
			return (typeof window.name != "undefined");
		},

		read : function () {
			return window.name;
		},

		save : function (serializedString) {
			window.name = serializedString;
		}

	});

	/* ******************************************************************** */

	/* Call auto-detect */
	implementation.detect();

	/*
	 * Delete the implementation object to free some memory. Otherwise
	 * it would be kept in memory due to the many closures (nested functions).
	 */
	implementation = null;

	/* Call the anonymous function: */
})(window, document);