One bear can do everything

/* Create a new XMLHttpRequest object to talk to the Web server */
var xmlHttp = false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
try {
  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
  try {
    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e2) {
    xmlHttp = false;
  }
}
@end @*/
if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
  xmlHttp = new XMLHttpRequest();

}
=====================

2.open the url with :get or post

xmlHttp.open("GET", url, true);

If u want to use 'POST' like:

xmlHttp.open("POST", url, true);
U should add use like :
----------
  // Open a connection to the server
  xmlHttp.open("POST", url, true);
  // Setup a function for the server to run when it's done
  xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
  //post method need this sentence
  xmlHttp.onreadystatechange = updatePage;
  // Send the request
  xmlHttp.send(postStr);
----------

3.Five Steps:五个步骤

=========

0：请求没有发出（在调用 open() 之前）。
1：请求已经建立但还没有发出（调用 send() 之前）。
2：请求已经发出正在处理之中（这里通常可以从响应得到内容头部）。
3：请求已经处理，响应中通常有部分数据可用，但是服务器还没有完成响应。
4：响应已完成，可以访问服务器响应并使用它。

=========
But Firefox and IE can only get: 1,2,3,4
Safari can only get:2,3,4

4.boldness error:莫名其妙的错误

If you add both "action=''" and "onsubmit=''" in one form like:

<form name="user" method="post" onsubmit="add_remember_date()" action='<?=site_url('/admin/action');?>'>

u can get some boresome error.
Suggest:u can cancel action like:

<form name="user" method="post"  onsubmit="add_remember_date()">

I am sure that there is no question.

5.About documet.user.submit();

If u have such sentence below in your code and want to use documet.user.submit():

<input type=”button” id=”submit”>

some error will happen ,so u can change id=’submit’ to id = ’submit_’

“submit” as the id name can take this error,so u should change to another name