我正在用 typescript 创建一个EventEmitter,但我想不出一种方法来执行以下操作:
说我有一个这样的界面:
interface EventEmitterSubscription { dispose(): void }
// here it is
interface EventEmitter<T extends { [key: string]: any }> {
onAnyEvent(callback: (event: { type: ???, payload: ??? }) => void): EventEmitterSubscription
// ...
}
我找不到一种方法来键入
onAnyEvent
回调,例如,对于这样的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,我的实现具有如下界面:
onAnyEvent(callback: (event: { type: keyof T, payload: T[keyof T] }) => void): EventEmitterSubscription
除非当前不起作用,例如会产生
onAnyEvent(callback: (event: { type: 'onNumberReceived', payload: number } | {type: 'onNumberReceived', payload: { cat: ICat } } | /* ... */) => void): EventEmitterSubscription
类型那么如何键入
onAnyEvent
字段? 最佳答案
创建联合的一种可能方法是具有一个映射类型,每个属性都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] } };
然后您可以定义通用联合类型
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