仿京东左侧菜单 hover效果-简易demo

简单描述： 用到的知识点 css 中的绝对定位 以及 Js 中的事件冒泡（或事件委托）

  .cont{display:inline-block;width:200px;height:200px;border:1px solid red;position:absolute;left:150px;top:2px;display:none;}

<div style="border:1px solid green;margin:30px auto;150px;" id="menu">
            
            <div class="item" id="div1" style="position:relative;">
                <span style="display:inline-block;background: #abcdef;150px;height:50px;cursor:pointer;">123</span>
                <span id="span1"  class="cont">
                     hello1111111
                     hello1111111
                     hello1111111
                     hello1111111
                     hello1111111
                </span>
            </div>
            
            <div id="div2" class="item" style="position:relative;">
                <span style="display:inline-block;background: red;150px;height:50px;cursor:pointer;">123</span>
                <span class="cont">hello222222</span>
            </div>
                
            <div id="div3" class="item" style="position:relative;">
                <span style="display:inline-block;background: green;150px;height:50px;cursor:pointer;">123</span>
                <span class="cont">hello333333</span>
            </div>
            
         </div>

 window.onload = function(){
             var oSpan1 = document.getElementById("span1");
             var oMenu = document.getElementById("menu");
             var oSMenu = oMenu.childNodes;
                  
             for(var n=oSMenu.length-1; n>=0; n--){
                  if(oSMenu[n].className == "item"){
                      oSMenu[n].onmouseover = function(evt){
                            var target = oTargetByClass._get_target_child(this.childNodes, "cont");
                            target.style.display = "block";
                      }
                      
                       oSMenu[n].onmouseout = function(evt){                    
                            var target = oTargetByClass._get_target_child(this.childNodes, "cont");
                            target.style.display = "none";
                     }         
                  }                 
             } 
                        
             var oTargetByClass = {
             
                 _get_target_child: function(childNodes, child_class){
                    for(var i = childNodes.length-1; i>=0; i--){
                        if(childNodes[i].className == child_class){
                             return childNodes[i];
                        }
                    } 
                 }
             }
         }