AJAX basic

        <pre data-sub="prettyprint:_">
        var xmlHttp = null;
        if (window.XMLHttpRequest) { // IE7, Mozilla, Safari, Opera, etc.
        xmlHttp = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
        try{
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); //IE 5.x, 6
        }
        catch(e) {}
        }

        function sendRequest(url) {
        if (xmlHttp) {
        xmlHttp.open("GET", url, true); // true = async
        xmlHttp.onreadystatechange = onCallback;
        xmlHttp.setRequestHeader('Content-type',
        'application/x-www-form-urlencoded');
        xmlHttp.send(null);
        }
        }

        function onCallback() {
        if (xmlHttp.readyState == 4) {
        if (xmlHttp.status == 200){
        var r = document.getElementById('results');
        r.innerHTML = xmlHttp.responseText;
        }
        else {
        alert('Error: ' + xmlHttp.status);
        }
        }
        }
        </pre>