(function () {
 var propertys = Object.keys(window);
 alert(propertys.length);   //3
 alert(propertys.join("n"));  //window,document,InstallTrigger,除了最后一个是火狐私有的属性,原来window对象只有两个可枚举的自身属性.window属性指向window对象自身,一般没什么用.
})()

(function () {
 var propertys = Object.getOwnPropertyNames(window);
 alert(propertys.length);  //72
 alert(propertys.join("n")); //Object,Function,eval等等
})()

(function () {
 var getEnumPropertyNames = function (obj) {
  var props = [];
  for (prop in obj) {
   props.push(prop);
  }
  return props;
 }
 var propertys = getEnumPropertyNames(window);
 alert(propertys.length);  //185
 alert(propertys.join("n")); //addEventListener,onload等等
})()

(function () {
 var getAllPropertyNames = function (obj) {
  var props = [];
  do {
   props = props.concat(Object.getOwnPropertyNames(obj));
  } while (obj = Object.getPrototypeOf(obj));
  return props;
 }
 var propertys = getAllPropertyNames(window);
 alert(propertys.length);   //276
 alert(propertys.join("n"));  //toString等
})()