static/tinymce/plugins/autosave/editor_plugin_src.js
function(ed) {
			var self = this, testKey = PLUGIN_NAME + '_test', testVal = "OK";

			self.key = PLUGIN_NAME + ed.id;

			// Loop though each storage engine type until we find one that works
			tinymce.each([
				function() {
					// Try HTML5 Local Storage
					if (localStorage) {
						localStorage.setItem(testKey, testVal);

						if (localStorage.getItem(testKey) === testVal) {
							localStorage.removeItem(testKey);

							return localStorage;
						}
					}
				},

				function() {
					// Try HTML5 Session Storage
					if (sessionStorage) {
						sessionStorage.setItem(testKey, testVal);

						if (sessionStorage.getItem(testKey) === testVal) {
							sessionStorage.removeItem(testKey);

							return sessionStorage;
						}
					}
				},

				function() {
					// Try IE userData
					if (tinymce.isIE) {
						ed.getElement().style.behavior = "url('#default#userData')";

						// Fake localStorage on old IE
						return {
							autoExpires : TRUE,

							setItem : function(key, value) {
								var userDataElement = ed.getElement();

								userDataElement.setAttribute(key, value);
								userDataElement.expires = self.getExpDate();

								try {
									userDataElement.save("TinyMCE");
								} catch (e) {
									// Ignore, saving might fail if "Userdata Persistence" is disabled in IE
								}
							},

							getItem : function(key) {
								var userDataElement = ed.getElement();

								try {
									userDataElement.load("TinyMCE");
									return userDataElement.getAttribute(key);
								} catch (e) {
									// Ignore, loading might fail if "Userdata Persistence" is disabled in IE
									return null;
								}
							},

							removeItem : function(key) {
								ed.getElement().removeAttribute(key);
							}
						};
					}
				},
			], function(setup) {
				// Try executing each function to find a suitable storage engine
				try {
					self.storage = setup();

					if (self.storage)
						return false;
				} catch (e) {
					// Ignore
				}
			});
		}
function(ed) {
			var self = this, testKey = PLUGIN_NAME + '_test', testVal = "OK";

			self.key = PLUGIN_NAME + ed.id;

			// Loop though each storage engine type until we find one that works
			tinymce.each([
				function() {
					// Try HTML5 Local Storage
					if (localStorage) {
						localStorage.setItem(testKey, testVal);

						if (localStorage.getItem(testKey) === testVal) {
							localStorage.removeItem(testKey);

							return localStorage;
						}
					}
				},

				function() {
					// Try HTML5 Session Storage
					if (sessionStorage) {
						sessionStorage.setItem(testKey, testVal);

						if (sessionStorage.getItem(testKey) === testVal) {
							sessionStorage.removeItem(testKey);

							return sessionStorage;
						}
					}
				},

				function() {
					// Try IE userData
					if (tinymce.isIE) {
						ed.getElement().style.behavior = "url('#default#userData')";

						// Fake localStorage on old IE
						return {
							autoExpires : TRUE,

							setItem : function(key, value) {
								var userDataElement = ed.getElement();

								userDataElement.setAttribute(key, value);
								userDataElement.expires = self.getExpDate();

								try {
									userDataElement.save("TinyMCE");
								} catch (e) {
									// Ignore, saving might fail if "Userdata Persistence" is disabled in IE
								}
							},

							getItem : function(key) {
								var userDataElement = ed.getElement();

								try {
									userDataElement.load("TinyMCE");
									return userDataElement.getAttribute(key);
								} catch (e) {
									// Ignore, loading might fail if "Userdata Persistence" is disabled in IE
									return null;
								}
							},

							removeItem : function(key) {
								ed.getElement().removeAttribute(key);
							}
						};
					}
				},
			], function(setup) {
				// Try executing each function to find a suitable storage engine
				try {
					self.storage = setup();

					if (self.storage)
						return false;
				} catch (e) {
					// Ignore
				}
			});
		}
This method will setup the storage engine. If the browser has support for it.

@method setupStorage