Could you please take a look at my code and give me a hint where the problem is?
Code:
ajaxRequest = function(u,f,m,b,h,s)
{
alert ('ajaxRequest');
this.url = u;
this.wState = f || function() { };
this.method = m || "GET";
this.body = b || null;
this.headers = h || false;
this.sync = s || true;
this.abortReq = false;
this.req = (window.XMLHttpRequest) //Gecko-Browser?
?
new XMLHttpRequest() //Gecko-Browser!
:
((window.ActiveXObject) //Internet Explorer?
?
new ActiveXObject("Microsoft.XMLHTTP") //Internet Explorer!
:
false //some Error occured
);
this.doRequest = function() //function to perform the request
{
alert('doRequest');
this.req.open(this.method,this.url,this.sync); //Open connection
if (this.headers) //additional headers given?
{
for (var i=0; i<this.headers.length; i+=2)
{
this.req.setRequestHeader(
this.headers[i],this.headers[i+1] //construct keyvalue pairs for the header
);
}
}
this.req.onreadystatechange = this.wState; //function-call
(!this.abortReq) ? this.req.send(this.body) : this.req.abort();
//send request if not aborted somehow
}
}
/**
* function to check whether the connection can
* be established for given username and password
*
* @param: string username Username
* @param: string password Password
*/
var checkConnection = function (username, password) {
xmlhttp = new ajaxRequest(
'http://url*****',
function()
{
alert('callback-function');
var r = xmlhttp.req;
if (r.readyState==4) //transfer complete
{
alert('readystate!')
document.getElementById('test-label').value =
(r.status == 200) //insert Data in DOM
? r.responseText : r.status+"ERROR"; //Error occured
alert ('responsetext inserted');
}
},
'POST', //type
'&username='+username+'&password='+password, //query
["Content-Type","application/x-www-form-urlencoded"] //header
);
xmlhttp.doRequest();
}
When I perform the query the debug messages appear in following order:
1.) ajaxRequest
2.) doRequest
3.) callback-function
4.) callback-function
5.) callback-function
6.) readystate!
7.) responsetext inserted (*it actually is updated*)
8.) callback-function
9.) readystate!
10.) responsetext inserted
11.) undefined (appears always)
My question is: Why is the callback-function called again (debug no.
and why do I always receive the alert-box "undefined", whithout calling any alert?!Thanks for your help in advance!