TypeScript - 從對象創建聯合

Question

我正在使用typescript創建一個EventEmitter，我無法找到一種方法來執行以下操作：

說我有這樣的界面：

interface EventEmitterSubscription { dispose(): void }

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

我找不到一種方法來輸入onAnyEvent回調，例如，對於像這樣的eventEmitter：

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

onAnyEvent字段將具有該類型

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

目前我的實現界面如下：

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

除了當前不起作用，例如會產生類型onAnyEvent(callback: (event: { type: 'onNumberReceived', payload: number } | { type: 'onNumberReceived', payload: { cat: ICat } } | /* ... */) => void): EventEmitterSubscription

那么如何鍵入onAnyEvent字段？

Answer 1

創建聯合的一種可能方法是使用映射類型，每個屬性具有所需聯合的一個元素的類型，如下所示：

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

然后，您可以定義通用聯合類型

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

並使用它

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