类型中缺少索引签名

Question

我正在尝试创建一个类型安全的 EventEmitter，但是我无法强制传递给泛型的接口是类型EventMap而不引发 TypeScript 抱怨。

type EventHandler = () => void
type EventMap = Record<string, EventHandler>

interface EventListener {
  handler: EventHandler
  once: boolean
}

export class Emitter<Events extends EventMap> {
  private listeners = new Map<keyof Events, EventListener[]>()

  private addListener<E extends keyof EventMap>(type: E, listener: EventListener) {
    const listeners = this.listeners.get(type) || []
    this.listeners.set(type, [...listeners, listener])
  }

  @bind
  public on<E extends keyof EventMap>(type: E, handler: Events[E]) {
    this.addListener(type, { handler, once: false })
  }
}


interface TestEvents {
  test: (a: number) => void,
}

class Test extends Emitter<TestEvents> {}

给我

Type 'TestEvents' does not satisfy the constraint 'Record<string, EventHandler>'.
Index signature is missing in type 'TestEvents'.

Answer 1

您需要对它进行稍微不同的约束，您希望 的所有键Events不一定EventHandlers都有Events索引签名。您可以使用以下内容：

type EventHandler = (...a: any[]) => void

interface EventListener {
    handler: EventHandler
    once: boolean
}

export class Emitter<Events extends Record<keyof Events, EventHandler>> {
    private listeners = new Map<keyof Events, EventListener[]>()

    private addListener<E extends keyof Events>(type: E, listener: EventListener) {
        const listeners = this.listeners.get(type) || []
        this.listeners.set(type, [...listeners, listener])
    }

    public on<E extends keyof Events>(type: E, handler: Events[E]) {
        this.addListener(type, { handler, once: false })
    }
}


interface TestEvents {
    test: (a: number) => void,
}

class Test extends Emitter<TestEvents> { }
new Test().on("test", a => a.toExponential) // a is number.

但是，这种方法存在一个问题，如果地图中有多个事件（您可能会这样做），打字稿将无法推断参数类型

interface TestEvents {
    test: (a: number) => void,
    test2: (a: number) => void,
}

class Test extends Emitter<TestEvents> { }
new Test().on("test", a => a.toExponential) // a is any

这是可以修复的，但是类型变得更加复杂，请参阅此处了解非常相似的想法。