I'm writing a small ajax class for personal use. In the class, I have a "post" method for sending post requests. The post method has a callback parameter. In the onreadystatechange propperty, I need to call the callback method.

Something like this:

this.requestObject.onreadystatechange = function() {
    callback(this.responseText); 
}

However, I can't access the callback variable from within the anonomous function. How can I bring the callback variable into the scope of the onreadystatechange anonomous function?

edit:

Here's the full code so far:

function request()
{
this.initialize = function(errorHandeler)
{
try {
try {
this.requestObject = new XDomainRequest();
} catch(e) {
try {
this.requestObject = new XMLHttpRequest();
} catch (e) {
try {
this.requestObject = new ActiveXObject("Msxml2.XMLHTTP"); //newer versions of IE5+
} catch (e) {
this.requestObject = new ActiveXObject("Microsoft.XMLHTTP"); //older versions of IE5+
}
}
} 
} catch(e) {
errorHandeler();
}
}


this.post = function(url,data)
{
var response;var escapedData = "";
if (typeof data == 'object') {
for (i in data) {
escapedData += escape(i)+'='+escape(data[i])+'&';
}
escapedData = escapedData.substr(0,escapedData.length-1);
} else {
escapedData = escape(data);
}
this.requestObject.open('post',url,true);
this.requestObject.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
this.requestObject.setRequestHeader("Content-length", data.length);
this.requestObject.setRequestHeader("Connection", "close");
this.requestObject.onreadystatechange = function()
{
if (this.readyState == 4) {
// call callback function
}
}
this.requestObject.send(data);
}