var foo = {a1:'1',a2:'2',a3:'3'};
//获得对象所有属性的数组
Object.getOwnPropertyNames(foo);
> [ 'a1', 'a2', 'a3' ]
//获取对象属性的个数
Object.getOwnPropertyNames(foo).length;
> 3
getOwnPropertyNames的浏览器支持
| Feature | Chrome | Firefox | Internet Explorer | Opera | Safari |
| Basic support | 5 | 4.0 | 9 | 12 | 5 |