XHR工厂的实现

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var
AjaxHandler = new
Interface("AjaxHandler",["request", "createXObject"]);

var
XHRFactory = function() {};

XHRFactory.prototype = function() {

    request: function(method, url, callback, postvar) {

        var
xhr = this.createXObject();

        xhr.onreadystatechange = function(){

            if(xhr.readyState == 4) {

                (xhr.status == 200)?(callback.success(xhr.responseText,xhr.ResponseXML)):(callback.failuse(xhr.status));

                xhr.open(method, url, callback);

                if(method !== "POST") postvar = null;

                xhr.send(postvar);

            }

        }

    },

    createXObject: function(){

        var
methods = [function(){return
new XMLHttpRequest()},

                       function(){return
new ActiveXObject("Microsoft.XMLHTTP")},

                       function(){return
new ActiveXObject("Msxml2.XMLHTTP")}

                       ];

        for(var
i = 0, len = methods.length; i < len; i++) {

            try{

                methods[i];

            }

            catch(e){

                continue;

            }

            this.createXObject() = methods[i];

            return
methods[i];

        }

        throw
new Error("Your explore dosen‘t support Ajax!‘");

    }

}