There is a strange problem when you reuse XMLHttpRequest for post data under Chrome.

var http_request; //is outside the declaration object, mainly in order to use    //in Updatepage without refreshing the content function post (URL, Parameter) {       if (http_request==null)     {         http_request = gethttprequest ();     }            if  (!http_request)        {        alert ("xmlhttprequest  initialization failed!");     }    else    {         //adds a rnd random number at the end of the URL so that it does not occur to read IE cache         if ( Url.indexof ("?")  > -1)         {             url = url +  "&rnd="  + math.random ();         }        else         {            url = url +   "? rnd="  + math.random ();        }                        http_request.open ("POST",  url, false);  //Open Request  //false  Synchronous, true  Async         http_request.onreadystatechange = updatepage; / /Set callback method         http_request.setrequestheader ("Content-length",  Parameter.length);         http_request.setrequestheader (' Content-Type ') ,  ' application/x-www-form-urlencoded ');         http_request.send ( parameter);  //Send Request      }}  //callback Method Function updatepage () {       if   (http_request.readystate == 4)     {            if (http_request.status == 200)                    {                      alert ("...");  / /        }    }}

The test found that, under Chrome 26, if a public variable was declared: Http_request

Then when the XMLHttpRequest is reused multiple times, if the parameter (content) is passed at post, the callback function is executed 2 times in a row: Updatepage ()

If the post has no arguments (content), only 1 callback functions will be executed: Updatepage ()

Tested under Firefox and IE, only 1 callback functions are performed: Updatepage ()

It's also easy to solve this problem with Chrome 26, which is re-initialized each time you use Http_request (XMLHttpRequest):

Http_request = Gethttprequest ();

There is a strange problem when you reuse XMLHttpRequest for post data under Chrome.