一个AJAX类代码

基本用法：

var ajax = new ajaxobj(url);
ajax.addlistener(200, function(r){
alert(r);
});
ajax.send();

也可以连续调用：

var ajax = new ajaxobj(url).addlistener(200, function(r){
alert(r);
}).send();

另外还支持自定义的post或get方式请求，以及监视不同的http状态码，自己看代码琢磨吧 :)
完整代码：

ajaxobj = function(url, method, content){
    this.r = null;
    this.url = url;
    this.method = method;
    this.content = content;
    this.header = {};
    this.header["connection"] = "close";
    this.header["content-type"] = "application/x-www-form-urlencoded";
    var self = this;
    if(window.xmlhttprequest){
        this.r = new xmlhttprequest();
    }else if(window.activexobject){
        try {
            this.r = new activexobject("msxml2.xmlhttp");
        } catch(e) {
            try{
                this.r = new activexobject("microsoft.xmlhttp");
            } catch(e) {
            }
        }
    }
    this.addlistener = function(http_status, func){
        if(!this.l)
            this.l=[];
        this.l[http_status] = func;
        return this;
    };
    this.setheader = function(name, value){
        this.header[name] = value;
        this.r.setrequestheader(name, value);
        return this;
    };
    this.send = function(){
        if(this.method != "post" && this.method != "get")
            this.method = "get";
        this.r.open(this.method, this.url, true);
        for(var h in this.header) {
            this.r.setrequestheader(h, this.header[h]);
        }
        this.r.send(this.content);
    };
    if(this.r) this.r.onreadystatechange = function(){
        if(self.r.readystate == 4 && self.l[self.r.status] != null)
            self.l[self.r.status](self.r.responsetext);
    };
};