Question

我在打字稿中创建了一个EventEmitter，但我无法找到一种方法来执行以下操作：

说我有这样的界面：

interface EventEmitterSubscription { dispose(): void }

// here it is
interface EventEmitter<T extends { [key: string]: any }> {
  onAnyEvent(callback: (event: { type: ???, payload: ??? }) => void): EventEmitterSubscription
  // ...
}

我无法找到键入onAnyEvent回调的方法，例如，对于像这样的eventEmitter：

EventEmitter<{ onNumberReceived: number, onCatReceived: { cat: ICat }, onPersonNameReceived: string }>

onAnyEvent字段的类型为

onAnyEvent(callback: (event: { type: 'onNumberReceived', payload: number } | { type: 'onCatReceived', payload: { cat: ICat } } | { type: 'onPersonNameReceived', payload: string }) => void): EventEmitterSubscription

目前我的实现界面如下：

onAnyEvent(callback: (event: { type: keyof T, payload: T[keyof T] }) => void): EventEmitterSubscription

除了目前不起作用之外，例如会生成类型onAnyEvent(callback: (event: { type: 'onNumberReceived', payload: number } | { type: 'onNumberReceived', payload: { cat: ICat } } | /* ... */) => void): EventEmitterSubscription

那么如何输入onAnyEvent字段？

Answer 1

创建联合的一种可能方法是使用映射类型，每个属性具有所需联合的一个元素的类型，如下所示：

type EventTypeMap<T extends { [key: string]: {} }> =
    { [K in keyof T]: { type: K; payload: T[K] } };

然后你可以定义泛型联合类型

type CallbackEventTypes<T extends { [key: string]: {} }> =
     EventTypeMap<T>[keyof EventTypeMap<T>]

并使用它

interface EventEmitterSubscription { dispose(): void }

interface EventEmitter<T extends { [key: string]: {} }> {
  onAnyEvent(callback: (event: CallbackEventTypes<T>) => void): EventEmitterSubscription
  // ...
}

interface ICat { meow() }

type Emitter = EventEmitter<{ onNumberReceived: number, onCatReceived: { cat: ICat }, onPersonNameReceived: string }>

type HandlerType = Emitter['onAnyEvent'];

// inferred as
//type HandlerType = 
// (callback: (event: { type: "onNumberReceived"; payload: number; }
//                  | { type: "onCatReceived"; payload: { cat: ICat; }; }
//                  | { type: "onPersonNameReceived"; payload: string; }
//            ) => void) => EventEmitterSubscription

TypeScript - 从对象

1 个答案: