## 問題 Problem 你想給一個類擴展新的功能或者替換掉老的。 You want to extend a class to add new functionality or replace old. ## 方案 Solution 使用`::`給對象或者類的原型賦值上你的新函數。 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' ~~~ ## 討論 Discussion 在JavaScript中（在CoffeeScript也一樣），對象有一個原型成員，定義了那些以此為原型的對象所有可用的成員方法。在CoffeeScript中，你可以使用`::`操作符來直接訪問原型。 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：**?盡管在像Ruby這樣的語言中，擴展原生的對象很常見，但是在JavaScript中這種行為被看作是不好的實踐（參看：?[Maintainable JavaScript: Don’t modify objects you don’t own](http://www.nczonline.net/blog/2010/03/02/maintainable-javascript-dont-modify-objects-you-down-own/)和[Extending built-in native objects. Evil or not?](http://perfectionkills.com/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](http://www.nczonline.net/blog/2010/03/02/maintainable-javascript-dont-modify-objects-you-down-own/);?[Extending built-in native objects. Evil or not?](http://perfectionkills.com/extending-built-in-native-objects-evil-or-not/)).