建構子- JavaScript - MDN Web Docs
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constructor（建構子）是個隨著class 一同建立並初始化物件的特殊方法。
SkiptomaincontentSkiptoselectlanguage給開發者的網頁技術文件JavaScriptJavaScript參考文件Classes建構子ArticleActions正體中文(繁體)ThispagewastranslatedfromEnglishbythecommunity.LearnmoreandjointheMDNWebDocscommunity.語法敘述示例規範瀏覽器相容性參見RelatedTopics
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語法敘述示例規範瀏覽器相容性參見建構子
constructor（建構子）是個隨著class一同建立並初始化物件的特殊方法。
語法constructor([arguments]){...}敘述一個class只能有一個稱為constructor的特殊物件。
如果一個class出現兩次以上的constructor，就會發生SyntaxError錯誤。
如果不指定建構子，就會使用預設的建構子。
示例使用constructor方法這段程式碼是從classessample擷取而來。
（線上範例）
classSquareextendsPolygon{
constructor(length){
//我們在這裡呼叫了class的建構子提供多邊形的長寬值
super(length,length);
//注意：在derivedclass中，super()必須在使用this以前被呼叫。
不這樣的話會發生錯誤。
this.name='Square';
}
getarea(){
returnthis.height*this.width;
}
setarea(value){
this.area=value;
}
}預設的建構子如上文所說：如果不指定建構子，就會使用預設的建構子。
對baseclasses而言，預設的建構子長得像這樣：
constructor(){}
對derivedclass而言，預設的建構子長得像這樣：
constructor(...args){
super(...args);
}規範SpecificationECMAScriptLanguageSpecification#sec-static-semantics-constructormethod瀏覽器相容性BCDtablesonlyloadinthebrowser參見
super()
classexpression(en-US)
classdeclaration(en-US)
Classes
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