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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。
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語法
var obj = { property( parameters… ) {}, *generator( parameters… ) {}, async property( parameters… ) {}, async* generator( parameters… ) {}, // with computed keys: [property]( parameters… ) {}, *[generator]( parameters… ) {}, async [property]( parameters… ) {}, // compare getter/setter syntax: get property() {}, set property(value) {} };
說明
這個簡短的語法和在 ECMAScript 2015 引入 getter 以及 setter 類似。
請看以下程式碼:
var obj = { foo: function() { /* code */ }, bar: function() { /* code */ } };
你可以把它縮減為:
var obj = { foo() { /* code */ }, bar() { /* code */ } };
產生器方法
產生器方法(Generator method)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
。Always useyield
in conjunction with the asterisk (*).
// Using a named property var obj2 = { g: function* () { var index = 0; while (true) yield index++; } }; // The same object using shorthand syntax var obj2 = { * g() { var index = 0; while (true) yield index++; } }; var it = obj2.g(); console.log(it.next().value); // 0 console.log(it.next().value); // 1
Async 方法
Async 方法 也可以透過簡短語法定義。
// Using a named property var obj3 = { f: async function () { await some_promise; } }; // The same object using shorthand syntax var obj3 = { async f() { await some_promise; } };
Async generator methods
Generator methods can also be async.
var obj4 = { f: async function* () { yield 1; yield 2; yield 3; } }; // The same object using shorthand syntax var obj4 = { async* f() { yield 1; yield 2; yield 3; } };
Method definitions are not constructable
All method definitions are not constructors and will throw a TypeError
if you try to instantiate them.
var obj = { method() {} }; new obj.method; // TypeError: obj.method is not a constructor var obj = { * g() {} }; new obj.g; // TypeError: obj.g is not a constructor (changed in ES2016)
範例
Simple test case
var obj = { a: 'foo', b() { return this.a; } }; console.log(obj.b()); // "foo"
Computed property names
The shorthand syntax also supports computed property names.
var bar = { foo0: function() { return 0; }, foo1() { return 1; }, ['foo' + 2]() { return 2; } }; console.log(bar.foo0()); // 0 console.log(bar.foo1()); // 1 console.log(bar.foo2()); // 2
規範
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Method definitions' in that specification. |
Standard | Initial definition. |
ECMAScript 2016 (ECMA-262) The definition of 'Method definitions' in that specification. |
Standard | Changed that generator methods should also not have a [[Construct]] trap and will throw when used with new . |
ECMAScript Latest Draft (ECMA-262) The definition of 'Method definitions' in that specification. |
Draft |
瀏覽器相容性
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Method definitions | Chrome Full support 39 | Edge Full support 12 | Firefox Full support 34 | IE No support No | Opera Full support 26 | Safari Full support 9 | WebView Android Full support 39 | Chrome Android Full support 39 | Firefox Android Full support 34 | Opera Android Full support 26 | Safari iOS Full support 9 | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
Async generator methods | Chrome Full support 63 | Edge No support No | Firefox Full support 55 | IE No support No | Opera Full support 50 | Safari No support No | WebView Android Full support 63 | Chrome Android Full support 63 | Firefox Android Full support 55 | Opera Android Full support 46 | Safari iOS No support No | Samsung Internet Android Full support 8.0 | nodejs
Full support
10.0.0
|
Async methods | Chrome Full support 55 | Edge Full support 15 | Firefox Full support 52 | IE No support No | Opera Full support 42 | Safari No support No | WebView Android Full support 55 | Chrome Android Full support 55 | Firefox Android Full support 52 | Opera Android Full support 42 | Safari iOS No support No | Samsung Internet Android Full support 6.0 | nodejs
Full support
7.6.0
|
Generator methods are not constructable (ES2016) | Chrome Full support 42 | Edge Full support 13 | Firefox Full support 43 | IE No support No | Opera Full support 29 | Safari No support No | WebView Android Full support 42 | Chrome Android Full support 42 | Firefox Android Full support 43 | Opera Android Full support 29 | Safari iOS No support No | Samsung Internet Android Full support 4.0 | nodejs ? |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- User must explicitly enable this feature.
- User must explicitly enable this feature.