December 2013
Intermediate to advanced
160 pages
2h 41m
Chinese
Content preview from JavaScript 深入精要
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存取屬性的時候，原始／字面值會被轉換成物件
不要對這個事實感到疑惑：你可以將字串、數字與布林字面值視為具有屬性的物件 [例如
true.toString()
]。當你將這些原始值當成物件，並且試著存取它的屬性時，JavaScript
會從原始值的建構式建立一個包裝物件，讓你可以存取這個包裝物件的屬性與方法。在你
完成屬性存取之後，包裝物件就會被捨棄。透過這種轉換方式，在我們編寫的程式中，原
始值就如同物件一般。事實上，當原始值被視為物件時，JavaScript 會將它轉換成物件，
讓你可以存取它的屬性，並且在它回傳值之後將它變回原始值。你需要瞭解的重點在於整
件事的過程，以及 JavaScript 在幕後為你完成了這件事。
字串：
Live Code（http://jsfiddle. net/javascript enlightenment/ kpfNk/ ）
<!DOCTYPE html><html lang="en"><body><script>
// 字串物件被視為物件
var stringObject = new String('foo');
console.log(stringObject.length); // log 3
console.log(stringObject['length']); // log 3
// 當字面值／原始字串被視為物件時，它會轉換成物件
var stringLiteral = 'foo';
console.log(stringLiteral.length); // log ...
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