判断页面是否被改动过的JavaScript代码

<script language="JavaScript">
//判断页面是否被改动过
var Flag=false;
function setFlagValue(){
if (Flag==true) return false;
Flag=true;
}
function CheckForm(){
var clInput = document.all.tags("input");
var clArea  = document.all.tags("textarea");
for (i=0;i<clInput.length;i++){

if (Flag ==true)
break;
switch (clInput.item(i).type){
case "text" :
if (clInput.item(i).value != clInput.item(i).defaultValue){
Flag = true;
break;
}
case "radio" :
if (clInput.item(i).checked != clInput.item(i).defaultChecked){
Flag = true;
break;
}
case "checkbox" :
if (clInput.item(i).checked != clInput.item(i).defaultChecked){
Flag = true;
break;
}
}
}
for (i=0;i<clArea.length;i++){
if (Flag ==true)
break;
if (clArea.item(i).value != clArea.item(i).defaultValue){
Flag = true;
break;
}
}
}
function Check(){
CheckForm();
if(Flag)
return !window.confirm("该页已经被修改/n是否保存？")
return true;
}
function on_load(){
document.forms[0].onsubmit = Check//CheckForm;
for(i=0;i<document.all.tags("select").length;i++){
document.all.tags("select").item(i).onchange = setFlagValue;
}
}
window.onload=on_load;
</script>