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。
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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 (ECMA-262) The definition of 'Method definitions' in that specification. |
Living Standard |
瀏覽器相容性
BCD tables only load in the browser