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。
这个交互式例子的源代码位于 GitHub 仓库中。如果你想对这个交互式的样例做出一些贡献,请克隆 https://github.com/mdn/interactive-examples 然后提一个 pull request 给我们。
语法
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) {} };
描述
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
生成器方法也可以用这种简写语法定义。使用它们时,
- 简写语法中的星号(*)必须出现在生成器名前,也就是说
* 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
Async 方法也可以使用简写语法来定义。
// 用有属性名的语法定义方法(ES6之前): var obj3 = { f: async function () { await some_promise; } }; // 同一个方法,简写语法: var obj3 = { async f() { await some_promise; } };
Async 生成器方法
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;
}
};
方法定义不是构造函数
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)
示例
简单示例
var obj = { a : "foo", b(){ return this.a; } }; console.log(obj.b()); // "foo"
计算的属性名
该简写语法还支持计算的属性名称作为方法名。
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
规范
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 |
浏览器兼容
浏览器兼容表是通过一些结构化的数据生成的。如果你想贡献一些兼容数据,请参阅
https://github.com/mdn/browser-compat-data 并将 pull request 发送给我们。
Update compatibility data on GitHub
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.