Object.defineProperty 有什么用...
var myObj = {someNum: 123};
Object.defineProperty(myObj, "anotherNum",
{value: 456, writable: true, enumerable: true, configurable: true});
alert(myObj.someNum + " " + myObj.anotherNum);
...如果我也可以...
var myObj = {someNum: 321};
myObj.anotherNum = 654;
alert(myObj.someNum + " " + myObj.anotherNum);