<p>不论鼠标指针穿过被选元素或其子元素，都会触发 mouseover 事件。</p>      <p>只有在鼠标指针穿过被选元素时，才会触发 mouseenter 事件。</p>     <div class="over" style="background-color:lightgray;padding:20px;width:40%;float:left">          <h2 style="background-color:white;">被触发的 Mouseover 事件：<span></span></h2>      </div>      <div class="enter" style="background-color:lightgray;padding:20px;width:40%;float:right">             <h2 style="background-color:white;">被触发的 Mouseenter 事件：<span></span></h2>      </div>      <script>        var x = 0,y = 0;        var div1 = document.getElementsByClassName("over")[0];        div1.addEventListener("mouseover",function(){            var span = this.getElementsByTagName("span")[0]            span.innerText = (x +=1);            span.style.cssText = "border:2px red solid;";        },false);                var div2 = document.getElementsByClassName("enter")[0];        div2.addEventListener("mouseenter",function(){            var span = this.getElementsByTagName("span")[0]            span.innerText = (y +=1);            span.style.cssText = "border:2px red solid;";        },false);    </script>