无法删除节点

点击删除 控制台报错Cannot read property 'parentNode' of undefined at del

代码如下

<script type="text/javascript">

window.onload = function() {

var tr = document.getElementsByTagName("tr");

for (var i = 0; i < tr.length; i++) {

tr[i].onmouseover = function() {

this.style.backgroundColor = '#f2f2f2';

}

tr[i].onmouseout = function() {

this.style.backgroundColor = '#fff';

}

}

} //1. 鼠标移到不同行上时背景色改为色值为 #f2f2f2，移开鼠标时则恢复为原背景色 #fff

var num = 2;

function add() {

num++;

var tr = document.createElement("tr");

var xh = document.createElement("td");

var xm = document.createElement("td");

var del = document.createElement("td");

xh.innerHTML = "xh00" + num;

xm.innerHTML = "<input value='请输入姓名'/>"; //?

del.innerHTML = "<a href='javascript:del(this)'>删除</a>";

var table = document.getElementById("table");

table.appendChild(tr);

tr.appendChild(xh);

tr.appendChild(xm);

tr.appendChild(del);

//插入节点

var tr = document.getElementsByTagName("tr");

for (var i = 0; i < tr.length; i++) {

tr[i].onmouseover = function() {

this.style.backgroundColor = '#f2f2f2';

}

tr[i].onmouseout = function() {

this.style.backgroundColor = '#fff';

}

}

}

function del(obj){

            var table = obj.parentNode.parentNode.parentNode;

var tr = obj.parentNode.parentNode;

table.removeChild(tr);

        }

</script>

调用函数用的<a href="javascript:del(this);">删除</a>

我的理解是 obj是a标签 obj.parentNode是td

 obj.parentNode.parentNode是tr

obj.parentNode.parentNode.parentNode是table

要删除table中的tr就是table.removeChild(tr);