类表达式是用来定义类的一种语法。和函数表达式相同的一点是,类表达式可以是命名也可以是匿名的。如果是命名类表达式,这个名字只能在类体内部才能访问到。JavaScript 的类也是基于原型继承的。
语法
const MyClass = class [className] [extends] { // class body };
描述
类表达式的语法和类语句的语法很类似,只是在类表达式中,你可以省略掉类名,而类语句中不能。
和类声明一样,类表达式中的代码也是强制严格模式的。
示例
使用类表达式
下面的代码使用类表达式语法创建了一个匿名类,然后赋值给变量 Foo。
let Foo = class { constructor() {} bar() { return "Hello World!"; } }; let instance = new Foo(); instance.bar(); // "Hello World!"
命名类表达式
如果你想在类体内部也能引用这个类本身,那么你就可以使用命名类表达式,并且这个类名只能在类体内部访问。
const Foo = class NamedFoo { constructor() {} whoIsThere() { return NamedFoo.name; } } let bar = new Foo(); bar.whoIsThere(); // "NamedFoo" NamedFoo.name; // ReferenceError: NamedFoo is not defined Foo.name; // "NamedFoo"
规范
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) Class definitions |
Standard | Initial definition. |
ECMAScript 2016 (ECMA-262) Class definitions |
Standard | |
ECMAScript 2017 (ECMA-262) Class definitions |
Standard | |
ECMAScript Latest Draft (ECMA-262) Class definitions |
Draft |
浏览器兼容性
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out
https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
class |
Chrome Full support 42 | Edge Full support 13 | Firefox Full support 45 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 42 | Chrome Android Full support 42 | Firefox Android Full support 45 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 4.0 | nodejs Full support 6.0.0
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.