EventTarget.ts

/**
 * Base class for objects that dispatches events.
 */
export class EventTarget {
  private _listeners: Record<string, Function[]> | undefined

  /**
   * Add an event listener
   * @return The self object, for chainability.
   */
  addEventListener(type: string, listener: Function): EventTarget {
    if (this._listeners === undefined) {
      this._listeners = {}
    }
    const listeners = this._listeners
    if (listeners[type] === undefined) {
      listeners[type] = []
    }
    if (!listeners[type].includes(listener)) {
      listeners[type].push(listener)
    }
    return this
  }

  /**
   * Check if an event listener is added
   */
  hasEventListener(type: string, listener: Function): boolean {
    if (this._listeners === undefined) {
      return false
    }
    const listeners = this._listeners
    if (listeners[type] !== undefined && listeners[type].includes(listener)) {
      return true
    }
    return false
  }

  /**
   * Check if any event listener of the given type is added
   */
  hasAnyEventListener(type: string): boolean {
    if (this._listeners === undefined) {
      return false
    }
    const listeners = this._listeners
    return listeners[type] !== undefined
  }

  /**
   * Remove an event listener
   * @return The self object, for chainability.
   */
  removeEventListener(type: string, listener: Function): EventTarget {
    if (this._listeners === undefined) {
      return this
    }
    const listeners = this._listeners
    if (listeners[type] === undefined) {
      return this
    }
    const index = listeners[type].indexOf(listener)
    if (index !== -1) {
      listeners[type].splice(index, 1)
    }
    return this
  }

  /**
   * Emit an event.
   * @return The self object, for chainability.
   */
  dispatchEvent(event: any): EventTarget {
    if (this._listeners === undefined) {
      return this
    }
    const listeners = this._listeners
    const listenerArray = listeners[event.type]
    if (listenerArray !== undefined) {
      event.target = this
      for (let i = 0, l = listenerArray.length; i < l; i++) {
        listenerArray[i].call(this, event)
      }
    }
    return this
  }
}