一个简单的AJAX请求类

<script type="text/javascript" src="ajaxrequest.js"></script>
<script type="text/javascript">
var ajaxobj=new AJAXRequest;    // 创建AJAX对象
ajaxobj.method="GET";   // 设置请求方式为GET
ajaxobj.url="default.asp"  // URL为default.asp
// 设置回调函数，输出响应内容
ajaxobj.callback=function(xmlobj) {
     document.write(xmlobj.responseText);
}
ajaxobj.send();    // 发送请求

// AJAX类
function AJAXRequest() {
    var xmlObj = false;
    var CBfunc,ObjSelf;
    ObjSelf=this;
    try { xmlObj=new XMLHttpRequest; }
    catch(e) {
        try { xmlObj=new ActiveXObject("MSXML2.XMLHTTP"); }
        catch(e2) {
            try { xmlObj=new ActiveXObject("Microsoft.XMLHTTP"); }
            catch(e3) { xmlObj=false; }
        }
    }
    if (!xmlObj) return false;
    this.method="POST";
    this.url;
    this.async=true;
    this.content="";
    this.callback=function(cbobj) {return;}
    this.send=function() {
        if(!this.method||!this.url||!this.async) return false;
        xmlObj.open (this.method, this.url, this.async);
        if(this.method=="POST") xmlObj.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
        xmlObj.onreadystatechange=function() {
            if(xmlObj.readyState==4) {
                if(xmlObj.status==200) {
                    ObjSelf.callback(xmlObj);
                }
            }
        }
        if(this.method=="POST") xmlObj.send(this.content);
        else xmlObj.send(null);
    }
}