原生js获取子元素、给元素增加div

//鼠标移入移出动画
window.onload = function () {
var el = document.createElement(‘div‘);
el.className = "bg";
var obj_lis = document.getElementById("list").getElementsByTagName("a");
for (i = 0; i < obj_lis.length; i++) {
obj_lis[i].onmouseover = function () {
this.appendChild(el);
}
}

}
//end鼠标移入移出动画