I have found somewhere a short howto for AJAX, and derived (rewritten) the smallest AJAX framework ever out of it:

var ajax = false;
if(window.XMLHttpRequest) ajax = new XMLHttpRequest();
else if(window.ActiveXObject) {
	try { ajax = new ActiveXObject("Msxml2.XMLHTTP"); }
	catch (e) {
		try { ajax = new ActiveXObject("Microsoft.XMLHTTP"); }
		catch (e) {}
	}
}

function ajaxGetContent(type, url, parameter, output_function) {
	if(!ajax) eval(output_function + '(false);');
	ajax.onreadystatechange = function() {
		if(output_function != 'void' && ajax.readyState == 4) {
			if(ajax.status == 200) eval(output_function + '(ajax.responseText);');
			else eval(output_function + '(false);');
		}
	}
	if(type == "post") {
		ajax.open('POST', url, true);
		ajax.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
		ajax.send(parameter);
	} else {
		ajax.open('GET', url + ((parameter.length > 0)?"?":"") + parameter, true);
		ajax.send(null);
	}
}

That’s short, isn’t it?

To get the data you want you have to simply call the function and define a function which will be called after the data arrives:

ajaxGetContent('post', '/myURL/index.php', 'a=b', 'myDataCallBack');

function myDataCallBack(myContent) {
	if(myContent == false) {
		// something went wrong
	} else {
		// have fun with your data
	}
}

And if you want to send data only and don’t care of the answer, use this syntax:

ajaxGetContent('post', '/myURL/index.php', 'a=b', 'void');

Some explanation:
- type = How to send the data (Parameters). “post” or “get”.
- url = Where to send it to.
- parameter = URL-style parameters. Never use a question mark!
- output_function = The function which will be called after the data is received.

This Tool is tested in Opera 9+10, Firefox 2+3 and MSIE 7+8.

Have fun!