Class Emitter

packages/editor/src/plugin/emitter.ts:3–133

export type Listener = (...args: any[]) => void

export class Emitter {
  static listenerCount(emitter: Emitter, type: string | number): number {
    return emitter.listenerCount(type)
  }

  static defaultMaxListeners: number = 10

  events: Record<string | number, Listener | Listener[]> = {}

  maxListeners: number | undefined = undefined

  eventsCount = 0

  listenerCount(type: string | number): number {
    const evlistener = this.events[type]

    if (typeof evlistener === 'function') {
      return 1
    } else if (evlistener !== undefined) {
      return evlistener.length
    }

    return 0
  }

  eventNames(): Array<string | number> {
    return Object.keys(this.events)
  }

  setMaxListeners(count: number): this {
    this.maxListeners = count
    return this
  }

  getMaxListeners(): number {
    return this.maxListeners ?? Emitter.defaultMaxListeners
  }

  emit(type: string | number, ...args: any[]): boolean {
    const handler = this.events[type]

    if (handler === undefined) return false

    if (typeof handler === 'function') {
      handler(...args)
    } else {
      const len = handler.length
      for (let i = 0; i < len; ++i) handler[i](...args)
    }

    return true
  }

  on(type: string | number, listener: Listener, prepend = false): this {
    let existing = this.events[type]
    if (existing === undefined) {
      // Optimize the case of one listener. Don't need the extra array object.
      this.events[type] = listener