方法定義- JavaScript

自ECMAScript 2015 開始，引入了一種於物件初始器（objects initializers）中定義方法的簡短語法。

是一個將函式指派予方法名稱的簡便方式。

SkiptomaincontentSkiptosearchSkiptoselectlanguage給開發者的網頁技術文件JavaScriptJavaScript參考文件Functions方法定義ChangelanguageViewinEnglishThispagewastranslatedfromEnglishbythecommunity.LearnmoreandjointheMDNWebDocscommunity.語法說明範例規範瀏覽器相容性參見方法定義 自ECMAScript2015開始，引入了一種於物件初始器（objectsinitializers）中定義方法的簡短語法。

是一個將函式指派予方法名稱的簡便方式。

語法varobj={ property(parameters…){}, *generator(parameters…){}, asyncproperty(parameters…){}, async*generator(parameters…){}, //withcomputedkeys: [property](parameters…){}, *[generator](parameters…){}, async[property](parameters…){}, //comparegetter/settersyntax: getproperty(){}, setproperty(value){} }; 說明這個簡短的語法和在ECMAScript2015引入getter以及setter類似。

請看以下程式碼： varobj={ foo:function(){ /*code*/ }, bar:function(){ /*code*/ } }; 你可以把它縮減為： varobj={ foo(){ /*code*/ }, bar(){ /*code*/ } }; 產生器方法產生器方法（Generatormethod）也可以透過簡短語法定義之。

用的時候： 簡短語法的星號（*）必須放在產生器方法的屬性名前面。

也就是說*g(){}能動但g*(){}不行； 非產生器方法的定義可能不會有yield關鍵字。

也就是說過往的產生器函式動不了、並拋出SyntaxError。

Alwaysuseyieldinconjunctionwiththeasterisk(*). //Usinganamedproperty varobj2={ g:function*(){ varindex=0; while(true) yieldindex++; } }; //Thesameobjectusingshorthandsyntax varobj2={ *g(){ varindex=0; while(true) yieldindex++; } }; varit=obj2.g(); console.log(it.next().value);//0 console.log(it.next().value);//1Async方法Async方法也可以透過簡短語法定義。

//Usinganamedproperty varobj3={ f:asyncfunction(){ awaitsome_promise; } }; //Thesameobjectusingshorthandsyntax varobj3={ asyncf(){ awaitsome_promise; } }; AsyncgeneratormethodsGeneratormethodscanalsobeasync. varobj4={ f:asyncfunction*(){ yield1; yield2; yield3; } }; //Thesameobjectusingshorthandsyntax varobj4={ async*f(){ yield1; yield2; yield3; } };MethoddefinitionsarenotconstructableAllmethoddefinitionsarenotconstructorsandwillthrowaTypeErrorifyoutrytoinstantiatethem. varobj={ method(){} }; newobj.method;//TypeError:obj.methodisnotaconstructor varobj={ *g(){} }; newobj.g;//TypeError:obj.gisnotaconstructor(changedinES2016) 範例Simpletestcasevarobj={ a:'foo', b(){returnthis.a;} }; console.log(obj.b());//"foo" ComputedpropertynamesTheshorthandsyntaxalsosupportscomputedpropertynames. varbar={ foo0:function(){return0;}, foo1(){return1;}, ['foo'+2](){return2;} }; console.log(bar.foo0());//0 console.log(bar.foo1());//1 console.log(bar.foo2());//2規範 Specification Status Comment ECMAScript2015(6thEdition,ECMA-262)Thedefinitionof'Methoddefinitions'inthatspecification. Standard Initialdefinition. ECMAScript2016(ECMA-262)Thedefinitionof'Methoddefinitions'inthatspecification. Standard Changedthatgeneratormethodsshouldalsonothavea[[Construct]]trapandwillthrowwhenusedwithnew. ECMAScript(ECMA-262)Thedefinitionof'Methoddefinitions'inthatspecification. 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