EventEmitter.ts

export class EventEmitter<T> {
  handlers = [] as ((payload: T) => void)[]
  addHandler(cb: (payload: T) => void) {
    if (this.handlers.indexOf(cb) === -1) {
      this.handlers.push(cb)
    }
  }
  removeHandler(cb: (payload: T) => void) {
    const index = this.handlers.indexOf(cb)
    if (index !== -1) {
      this.handlers.splice(index, 1)
    }
  }
  emit(payload: T) {
    this.handlers.forEach(handler => handler(payload))
  }
}