创建http_request对象

function createAjaxObj() {
    var http_request = false;
    if (window.XMLHttpRequest) { // Mozilla, Safari,
        http_request = new XMLHttpRequest();
        if (http_request.overrideMimeType) {
            http_request.overrideMimeType('text/xml');
        }
    } else if (window.ActiveXObject) { // IE
        try {
            http_request = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                http_request = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {}
        }
    }
    return http_request;
}

http_request对象的使用

    function ajax_add(obj) {
        var http_request = createAjaxObj();
        var feedURL = obj.feedURL;
        var feedName = obj.feedName;
        http_request.onreadystatechange = function() {
            if (http_request.readyState == 4) {
                if (http_request.status == 200) {
                    //接收服务器返回信息responseText或responseXML
                    var text_data = http_request.responseText;
                    var parentNode = document.getElementById("leftcolumn");
                    var newDiv = document.createElement("div");
                    newDiv.innerHTML = unescape(text_data);
                    parentNode.appendChild(newDiv);
                    waiting.innerHTML = "";
                }
            }
        }
        var submitURL = "add_rss.php";
        http_request.open("POST", submitURL, true);
        http_request.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
        http_request.send("feedURL="+feedURL.value+"&feedName="+escape(feedName.value));
        var waiting = document.getElementById("waiting");
        waiting.innerHTML = "正在载入";
        //http_request.send(null);
    }