扩展内置对象 Extending Built-in Objects

问题 Problem

你想给一个类扩展新的功能或者替换掉老的。

You want to extend a class to add new functionality or replace old.

方案 Solution

使用::给对象或者类的原型赋值上你的新函数。

Use :: to assign your new function to the prototype of the object or class.

String::capitalize = () ->
  (this.split(/\s+/).map (word) -> word[0].toUpperCase() + word[1..-1].toLowerCase()).join ' '

"foo bar     baz".capitalize()
# => 'Foo Bar Baz'

讨论 Discussion

在JavaScript中（在CoffeeScript也一样），对象有一个原型成员，定义了那些以此为原型的对象所有可用的成员方法。在CoffeeScript中，你可以使用::操作符来直接访问原型。

Objects in JavaScript (and thus, in CoffeeScript) have a prototype member that defines what member functions should be available on all objects based on that prototype. In CoffeeScript, you can access the prototype directly via the :: operator.

注意： 尽管在像Ruby这样的语言中，扩展原生的对象很常见，但是在JavaScript中这种行为被看作是不好的实践（参看： Maintainable JavaScript: Don’t modify objects you don’t own和Extending built-in native objects. Evil or not?）。

Note: Although it’s quite common in languages like Ruby, extending native objects is often considered bad practice in JavaScript (see: Maintainable JavaScript: Don’t modify objects you don’t own; Extending built-in native objects. Evil or not?).