id怎么建立矩形選區？

1 2 3 window.onload = function () { var btn = document.getElementById("btn1"); btn.onclick = function() { insertEle(); } }function insertEle() { var oTest = document.getElementById("div1"); var newNode = document.createElement("div"); var reforeNode = document.getElementById("2"); oTest.insertBefore(newNode,reforeNode.nextSibling);}