jquery的封装

(function(window,undefined){
    var jQuery = function(){
        
    }
    window.jQuery=window.$=jQuery
})(window)

(function(window,undefined){
    var jQuery = function(selector){
   var elements = document.querySelectorAll(selector)
   for(var i=0;i<elements.length;i++){
       this[i] = elements[i]
   }
   this.length = elements.length
    }
    window.jQuery = window.$ = jQuery
})(window)