如何向(JSON)对象的原型添加方法

假设我从服务器接收到一些JSON对象，例如Person对象的一些数据:

{firstName: "Bjarne", lastName: "Fisk"}

现在，我想在这些数据之上有一些方法，例如计算全名:

fullName: function() { return this.firstName + " " + this.lastName; }

这样我就可以

var personData = {firstName: "Bjarne", lastName: "Fisk"};
var person = PROFIT(personData);
person.fullName(); // => "Bjarne Fisk"

What I basically would want to do here, is to add a method to the object's prototype. The fullName() method is general, so should not be added to the data object itself. Like..:

personData.fullName = function() { return this.firstName + " " + this.lastName; }

... 会导致大量冗余；而且可以说是"污染"了数据对象.

将此类方法添加到简单数据对象的当前最佳实践方式是什么？

EDIT:个

Slightly off topic, but if the problem above can be solved, it would be possible to do some nice pseudo-pattern matching like this:

if ( p = Person(data) ) {
   console.log(p.fullName());
} else if ( d = Dog(data) ) {
   console.log("I'm a dog lol. Hear me bark: "+d.bark());
} else {
   throw new Exception("Shitty object");
}

Person and Dog will add the methods if the data object has the right attributes. If not, return falsy (ie. data does not match/conform).

BONUS QUESTION: Does anyone know of a library that either uses or enables this (ie makes it easy)? Is it already a javascript pattern? If so, what is it called; and do you have a link that elaborates? Thanks :)