方法一:
 代码如下:
  New Document   window.onload = function(){
 var tags = document.getElementsByTagName("*"),
 count = tags.length, time, ret = {}, id;
 time = new Date();
 for(var i = 0; i < count; i++){
 id = tags[i].id;
 if(id){
 if(ret[id]){
 alert(id + "/n用时:" + (new Date() - time));
 return;
 }else{
 ret[id] = true;
 }
 }
 }
 alert("未找到相同ID");
 }
  script> 
 (function(){
 var html = [], rnd = parseInt(Math.random() * 1000);
 for(var i = 0; i < 1000; i++){
 html.push("" + i + "");
 };
 //在随机位置插入一个随机的id
 i = parseInt(Math.random() * 1000);
 html[i] = html[i] + ("" + rnd + "");
 document.write(html.join(""));
 })();
  script>
方法二:
 代码如下:
  New Document   function createDiv(){
 var html = [], id;
 for(var i = 0; i < 2000; i++){
 id = "divId" + parseInt(Math.random() * 10000);
 html.push("" + id + "");
 }
 document.body.innerHTML = html.join("");
 }
 window.onload = function(){
 createDiv();
 var oID = {} , result = {}, arr = [],
 tags = document.getElementsByTagName("*");
 for(var i = 0, id; i < tags.length; i++){
 id = tags[i].id;
 if(id){
 oID[id] = oID[id] ? oID[id] + 1 : 1;
 if(oID[id] > 1){
 result[id] = id + " " + oID[id]; } } } for(var o in result){
 arr.push(result[o]);
 }
 alert(arr.join("/t"));
 };
  script>
 
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