Ajax之工厂模式封装XMLHttpRequest

如下是对XMLHttpRequest的封装，为一个简易的工厂模式/* AjaxHandler interface. */var AjaxHandler = new Interface('AjaxHandler', ['request', 'createXhrObject']);/* SimpleHandler class. */var SimpleHandler = function() {}; // implements AjaxHandlerSimpleHandler.prototype = {  request: function(method, url, callback, postVars) {    var xhr = this.createXhrObject();    xhr.onreadystatechange = function() {      if(xhr.readyState !== 4) return;      (xhr.status === 200) ?         callback.success(xhr.responseText, xhr.responseXML) :         callback.failure(xhr.status);    };    xhr.open(method, url, true);    if(method !== 'POST') postVars = null;    xhr.send(postVars);  },  createXhrObject: function() { // Factory method.    var methods = [      function() { return new XMLHttpRequest(); },      function() { return new ActiveXObject('Msxml2.XMLHTTP'); },      function() { return new ActiveXObject('Microsoft.XMLHTTP'); }    ];        for(var i = 0, len = methods.length; i < len; i++) {      try {        methods[i]();      }      catch(e) {        continue;      }      // If we reach this point, method[i] worked.      this.createXhrObject = methods[i]; // Memoize the method.      return methods[i];    }        // If we reach this point, none of the methods worked.    throw new Error('SimpleHandler: Could not create an XHR object.');  } };/* Usage. */var myHandler = new SimpleHandler();var callback = {   success: function(responseText) { alert('Success: ' + responseText); },   failure: function(statusCode) { alert('Failure: ' + statusCode); } };myHandler.request('GET', 'script.php', callback);

如下是辅助类的实现：

// Constructor.var Interface = function(name, methods) {    if(arguments.length != 2) {        throw new Error("Interface constructor called with " + arguments.length          + "arguments, but expected exactly 2.");    }        this.name = name;    this.methods = [];    for(var i = 0, len = methods.length; i < len; i++) {        if(typeof methods[i] !== 'string') {            throw new Error("Interface constructor expects method names to be "               + "passed in as a string.");        }        this.methods.push(methods[i]);            }    };    // Static class method.Interface.ensureImplements = function(object) {    if(arguments.length < 2) {        throw new Error("Function Interface.ensureImplements called with " +           arguments.length  + "arguments, but expected at least 2.");    }    for(var i = 1, len = arguments.length; i < len; i++) {        var interface = arguments[i];        if(interface.constructor !== Interface) {            throw new Error("Function Interface.ensureImplements expects arguments "                 + "two and above to be instances of Interface.");        }                for(var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {            var method = interface.methods[j];            if(!object[method] || typeof object[method] !== 'function') {                throw new Error("Function Interface.ensureImplements: object "                   + "does not implement the " + interface.name                   + " interface. Method " + method + " was not found.");            }        }    } };