可以在 Typescript 中扩展类型吗?

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假设我有以下类型:

type Event = { name: string; dateCreated: string; type: string; }

我现在想扩展这种类型，即

I now want to extend this type, i.e.

type UserEvent extends Event = { UserId: string; }

这不起作用.我该怎么做?

This doesn't work. How can I do this?

推荐答案

关键字 extends 只能用于接口和类.

The keyword extends can be used for interfaces and classes only.

如果您只想声明具有附加属性的类型，可以使用 交叉路口类型:

If you just want to declare a type that has additional properties, you can use intersection type:

type UserEvent = Event & {UserId: string}

UPDATE 对于 TypeScript 2.2，现在可以有一个界面扩展类对象类型，如果类型满足一些限制:

UPDATE for TypeScript 2.2, it's now possible to have an interface that extends object-like type, if the type satisfies some restrictions:

type Event = { name: string; dateCreated: string; type: string; } interface UserEvent extends Event { UserId: string; }

反过来不行 - UserEvent 必须声明为接口，而不是 type 如果你想使用 extends 语法.

It does not work the other way round - UserEvent must be declared as interface, not a type if you want to use extends syntax.

而且仍然无法使用 extend 任意类型 - 例如，如果 Event 是没有任何约束的类型参数，则它不起作用.

And it's still impossible to use extend with arbitrary types - for example, it does not work if Event is a type parameter without any constraints.