从ECMAScript 2015开始,在对象初始器中引入了一种更简短定义方法的语法,这是一种把方法名直接赋给函数的简写方式。
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.
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) {}
};
该简写语法与ECMAScript 2015的getter和setter语法类似。
如下代码:
var obj = {
foo: function() {
/* code */
},
bar: function() {
/* code */
}
};
现可被简写为:
var obj = {
foo() {
/* code */
},
bar() {
/* code */
}
};
注意:简写语法使用命名函数而不是匿名函数(如…foo: function() {}
…)。命名函数可以从函数体调用(这对匿名函数是不可能的,因为没有标识符可以引用)。详细信息,请参阅function
。
生成器方法也可以用这种简写语法定义。使用它们时,
* g(){}
可以正常工作,而g *(){}
不行。非生成器方法定义可能不包含yield
关键字。这意味着遗留的生成器函数也不会工作,并且将抛出 SyntaxError
。始终使用yield
与星号(*)结合使用。
// 用有属性名的语法定义方法(ES6之前):
var obj2 = {
g: function*() {
var index = 0;
while(true)
yield index++;
}
};
// 同一个方法,简写语法:
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 方法也可以使用简写语法来定义。
// 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;
}
};
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;
}
};
所有方法定义不是构造函数,如果您尝试实例化它们,将抛出TypeError
。
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)
var obj = {
a : "foo",
b(){ return this.a; }
};
console.log(obj.b()); // "foo"
速记语法还支持计算的属性名称。
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
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) Method definitions |
Standard | Initial definition. |
ECMAScript 2016 (ECMA-262) Method definitions |
Standard | Changed that generator methods should also not have a [[Construct]] trap and will throw when used with new . |
ECMAScript Latest Draft (ECMA-262) Method definitions |
Draft |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Method definitions | Chrome Full support 39 | Edge Full support Yes | Firefox Full support 34 | IE No support No | Opera Full support 26 | Safari No support No | WebView Android Full support 39 | Chrome Android Full support 39 | Edge Mobile Full support Yes | Firefox Android Full support 34 | Opera Android Full support 26 | Safari iOS No support No | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
Generator methods are not constructable (ES2016) | Chrome ? | Edge ? | Firefox Full support 43 | IE No support No | Opera ? | Safari No support No | WebView Android ? | Chrome Android ? | Edge Mobile ? | Firefox Android Full support 43 | Opera Android ? | Safari iOS No support No | Samsung Internet Android ? | nodejs ? |
Async methods | Chrome ? | Edge ? | Firefox Full support 52 | IE No support No | Opera ? | Safari No support No | WebView Android ? | Chrome Android ? | Edge Mobile ? | Firefox Android Full support 52 | Opera Android ? | Safari iOS No support No | Samsung Internet Android ? | nodejs
Full support
7.6.0
|
Async generator methods | Chrome ? | Edge ? | Firefox Full support 55 | IE No support No | Opera ? | Safari No support No | WebView Android ? | Chrome Android ? | Edge Mobile ? | Firefox Android Full support 55 | Opera Android ? | Safari iOS No support No | Samsung Internet Android ? | nodejs
Full support
10.0.0
|