http = getHTTPObject();

function getHTTPObject(){
        var xmlhttp;

        /*@cc_on

        @if (@_jscript_version >= 5)
                try {
                        xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
                }catch(e){
                        try{
                        xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
                }catch(E){
                        xmlhttp = false;
                }
        }
        @else
                xmlhttp = false;
        @end @*/

        if(!xmlhttp && typeof XMLHttpRequest != 'undefined'){
                try {
                        xmlhttp = new XMLHttpRequest();
                }catch(e){
                        xmlhttp = false;
                }
        }

        return xmlhttp;
}

function doMath(){
	var url = "/ajaxtutorial/backend.php?op=" + document.getElementById('op').value;
	url += "&num1=" + document.getElementById('num1').value;
	url += "&num2=" + document.getElementById('num2').value;

        http.open("GET", url, true);
        http.onreadystatechange = handleHttpResponse;

        http.send(null);
}

function handleHttpResponse(){
        if(http.readyState == 4){
		document.getElementById('answer').innerHTML = http.responseText;
	}
}