storage with functional mixins

mixinStorage.js

function withStorage() {

  if (window.localStorage) {
    localStorage.call(this);
  } else if (document.documentElement.addBehavior) {
    userData.call(this);
  } else {
    memory.call(this);
  }

  this.encode = function(val) {
    return JSON.stringify(val);
  };

  this.decode = function(val) {
    return JSON.parse(val);
  };

  /****************html5 local storage***************/
  function localStorage() {

    this.initialize = function() {//...

    this.getItem = function(key) {
      return this.decode(window.localStorage.getItem(this.prefix + key));
    }

    this.setItem = function(key, val) {
      return window.localStorage.setItem(this.prefix + key, this.encode(val));
    }

    this.removeItem = function(key) {
      return window.localStorage.removeItem(this.prefix + key);
    }

    this.keys = function() {//...

    this.clear = function() {//...

    this.clearAll = function() {//...
  }

  /****************earlier IE ersatz storage***************/
  function userData() {

    this.initialize = function(namespace) {

      if (//...) {
        this.createStorageElement();
      }

      this.xmlDoc = this.dataStore.xmlDocument;
      this.xmlDocEl = this.xmlDoc.documentElement;

      //...
    }
  
    this.createStorageElement = function() {
      this.dataStore = document.createElement('div');
      //...
    }  

    this.getItem = function(key) {
      return this.decode(//...);
    }

    this.setItem = function(key, val) {
      return this.encode(//...);
    }

    this.keys = function() {//...

    this.clear = function() {//...

    this.clearAll = function() {//...
  }

  /****************temporary hash storage only***************/  
  function memory() {
    this.initialize = function(namespace) {
      //..

      if (!this.memoryStore) {
        this.memoryStore = {};
      }

      //..
    }

    this.getItem = function(key) {
      return this.decode(this.memoryStore[key]);
    }

    this.setItem = function(key, val) {
      return this.memoryStore[key] = this.encode(val);
    }

    this.keys = function() {//...

    this.clear = function() {//...

    this.clearAll = function() {//...
  }
}