一个简单的AJAX调用函数

function createXMLHttpRequest() {
    var request = false;
    if(window.XMLHttpRequest) {
        request = new XMLHttpRequest();
        if(request.overrideMimeType) {
            request.overrideMimeType('text/xml');
        }
    } else if(window.ActiveXObject) {
        var versions = ['Microsoft.XMLHTTP', 'MSXML.XMLHTTP', 'Microsoft.XMLHTTP',

'Msxml2.XMLHTTP.7.0', 'Msxml2.XMLHTTP.6.0', 'Msxml2.XMLHTTP.5.0',

'Msxml2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP'];
        for(var i=0; i<versions.length; i++) {
            try {
                request = new ActiveXObject(versions[i]);
                if(request) {
                    return request;
                }
            } catch(e) {}
        }
    }
    return request;
}

function ajax(xmlhttp,_method, _url, _param, _callback) {
    if (typeof xmlhttp == 'undefined') return;
    xmlhttp.onreadystatechange = function() {
        if (xmlhttp.readyState==4 && xmlhttp.status==200) {
            _callback(xmlhttp);
        }
    }
    xmlhttp.open(_method, _url, true);
    if (_method == "POST") {
        xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        xmlhttp.setRequestHeader("Content-Length", _param.length);
        xmlhttp.send(_param);
    }
    else {
        xmlhttp.send(null);
    }
}


//使用举例

var xmlhttp = createXMLHttpRequest();
var t1; //用来作超时处理


function adduserok(request) {
    alert(request.responseText);
    if (t1) clearTimeout(t1);
}

function connecttoFail() {
    if (xmlhttp) xmlhttp.abort();
    alert ('Time out');
}

if (xmlhttp) {
    ajax(xmlhttp,"POST", "","act=do&user=abc",adduserok);
    t1 = setTimeout(connecttoFail,30000);
}
else {
    alert ("Init xmlhttprequest fail");
}

很简单的两个函数，感觉比起那些原型库来方便多了。也没封装类，那个叫累啊。这么写自己需要什么功能再加就可以了，很容易。初始化对象之所以独立为一个函数是为了要处理超时，使得可以在需要时候取消掉xmlhttp的请求。