JavaScript 设计模式 － Factory(工厂模式) - 运行时确定创建对象

javascript-factory-xhr.js

var SimpleHandler = function() { };

SimpleHandler.prototype = {
  request: function(method, url, callback, postVars) {
    var xhr = this.createXhrObject();
    xhr.onreadystatechange = function() {
      // do some things
    };
    xhr.open(method. url, true);
    xhr.send(postVars);
  },
  createXhrObject: function() {
    var methods = [
      function() { return new XMLHttpRequest(); },
      function() { return new ActiveObject("Msxml2.XMLHTTP"); },
      function() { return new ActiveObject("Miscrosoft.XMLHTTP"); }
    ];

    for(var i=0, len = methods.lenght; i < len; i++ ) {
      try {
        methods[i](); 
      } catch(e) {
        continue;
      }

      // 修改自己 以免再次执行上面的检测代码
      this.createXhrObject = methods[i]; // Memoize the method
      return methods[i];
    }
  };
}