事件冒泡

    <div id="parent">
        <div id="child">
        </div>
    </div>

    <script>
        var parent =document.getElementById("parent");
        var child = document.getElementById("child")
        parent.onclick = function(event){
            alert("parent");
            // event.stopPropagation();
        }
        child.onclick  = function(event){
            alert("child")
            event.stopPropagation();
        }
        /* 如何阻止 event.stopPropagation(); */
    </script>