jQuery like data function in vanilla JavaScript

elwrap.js

    /**
     *
     * Element wrapper, necessary
     * for attaching custom user
     * data to element.
     *
     * It acts like jQuery wrapper
     * -creates an instance of wrapper
     * with element as zero field
     * providing access to `data`
     * method.
     *
     * Example usage:
     *
     * elwrap('#element').data('someKey') ===> returns undefined if niether elwrap('#element').data('someKey') was
     * previously set or #element doesn't have data-someKey attribute (just like jQuery does)
     * 
     * elwrap('#element').data('someKey', 'someValue') ===> sets value for given key to wrapper of #element, returning reference to wrapper object
     * (just like jQuery) so you can use multiple set in one line: elwrap('#element').data('someKey', 'someValue').data( 'someKey2', 'someValue2' ).data('someKey3', 'someValue3')
     * so you can acces them with:
     *
     * elwrap('#element').data('someKey')
     *
     *
    */
    window.elwrap = window.elwrap || (function(w,d){
      var Wrapper = function(element){
        this[0]   = element;
        var dataStore = {};

        this.data = function(key, value){
          if (typeof value === typeof undefined) {
            return dataStore[key] || this[0].getAttribute('data-' + key);
          } else {
            dataStore[key] = value;
            return this;
          }
        }
      },
      
      created = [];
      
      return function(elem){
        if (typeof elem === 'string') {
          //you can safely strip next 4 lines as IE<8 usage is insignificant
          if (!d.querySelector) {
            throw new Error('Browsers without document.querySelector/querySelectorAll (IE<8) should have dom Element reference as argument.');
            return false;
          }
          elem = d.querySelector(elem);
        }
        var tmpLength = created.length;
        for(var i = 0; i<tmpLength; i++){
          if (elem === created[i][0]) {
            return created[i];
          }
        }
        var fresh = new Wrapper(elem);
        created.push(fresh);
        return fresh;
      }
      
      
    })(window,document);