@glidejs/glide/src/core/event/events-bus.js

Glide.js is a dependency-free JavaScript ES6 slider and carousel. It’s lightweight, flexible and fast. Designed to slide. No less, no more

import { isArray } from '../../utils/unit'

export default class EventsBus {
  /**
   * Construct a EventBus instance.
   *
   * @param {Object} events
   */
  constructor (events = {}) {
    this.events = events
    this.hop = events.hasOwnProperty
  }

  /**
   * Adds listener to the specifed event.
   *
   * @param {String|Array} event
   * @param {Function} handler
   */
  on (event, handler) {
    if (isArray(event)) {
      for (let i = 0; i < event.length; i++) {
        this.on(event[i], handler)
      }

      return
    }

    // Create the event's object if not yet created
    if (!this.hop.call(this.events, event)) {
      this.events[event] = []
    }

    // Add the handler to queue
    const index = this.events[event].push(handler) - 1

    // Provide handle back for removal of event
    return {
      remove () {
        delete this.events[event][index]
      }
    }
  }

  /**
   * Runs registered handlers for specified event.
   *
   * @param {String|Array} event
   * @param {Object=} context
   */
  emit (event, context) {
    if (isArray(event)) {
      for (let i = 0; i < event.length; i++) {
        this.emit(event[i], context)
      }

      return
    }

    // If the event doesn't exist, or there's no handlers in queue, just leave
    if (!this.hop.call(this.events, event)) {
      return
    }

    // Cycle through events queue, fire!
    this.events[event].forEach((item) => {
      item(context || {})
    })
  }
}