类型安全的EventEmitter

[jiangshanmeta]

type MakeArray<T> = T extends any[] ? T : [T];

type EventMap<T> = {
  // 支持函数自定义个参数
  [K in keyof T]?: ((...args: MakeArray<T[K]>) => void)[];
};

export default class EventEmitter<T> {
  private _events: EventMap<T> = {};

  public on<E extends keyof T>(type: E, fn: (...rest: MakeArray<T[E]>) => void) {
    if (!this._events[type]) {
      this._events[type] = [];
    }
    this._events[type]?.push(fn);
  }

  public emit<E extends keyof T>(type: E, ...args: MakeArray<T[E]>) {
    const fns = this._events[type];
    fns?.forEach((fn) => {
      fn(...args);
    });
  }

  public off<E extends keyof T>(type: E, fn: (...args: MakeArray<T[E]>) => void) {
    this._events[type] = this._events[type]?.filter((item) => item !== fn);
  }
}

const event = new EventEmitter<{
  empty: [];
  one: string;
  multi: [number, string];
}>();

// 不需要额外参数，多传参会报错
event.emit('empty')
// 只能传一个 string类型的参数 注意上面 泛型参数也可以写为 one: [string]
event.emit('one','a')
// 需要两个参数
event.emit('multi',1,'')