Ajax核心

function getHTTPObject() {
    if (typeof XMLHttpRequest == "undefined")
        XMLHttpRequest = function () {
            try { return new ActiveXObject("Msxml2.XMLHTTP.6.0"); }
            catch (e) { }
            try { return new ActiveXObject("Msxml2.XMLHTTP.3.0"); }
            catch (e) { }
            try { return new ActiveXObject("Msxml2.XMLHTTP"); }
            catch (e) { }
            return false;

        }
    return new XMLHttpRequest();
}

function getNewContent() {
    var request = getHTTPObject();
    if (request) {
        request.open("GET", "example.txt", true);
        request.onreadystatechange = function () {
            if (request.readyState == 4) {
                var para = document.createElement("p");
                var txt = document.createTextNode(request.responseText);
                para.appendChild(txt);
                document.getElementById("new").appendChild(para);
            }
        };
        request.send(null);
    } else {
        alert("Sorry,your browser dosen\'t support XMLHttpRequest");
    }
    
}