substance/dom/DOMEventListener.js

Substance is a JavaScript library for web-based content editing. It provides building blocks for realizing custom text editors and web-based publishing system. It is developed to power our online editing platform [Substance](http://substance.io).

import isFunction from '../util/isFunction'
import isString from '../util/isString'
import findIndex from '../util/findIndex'

/*
  Internal implementation used to store event bindings.
*/
export default class DOMEventListener {
  constructor (eventName, handler, options) {
    /* istanbul ignore next */
    if (!isString(eventName) || !isFunction(handler)) {
      throw new Error("Illegal arguments: 'eventName' must be a String, and 'handler' must be a Function.")
    }
    options = options || {}
    var origHandler = handler
    var context = options.context
    var capture = Boolean(options.capture)

    if (context) {
      handler = handler.bind(context)
    }
    if (options.once === true) {
      handler = _once(this, handler)
    }

    this.eventName = eventName
    this.originalHandler = origHandler
    this.handler = handler
    this.capture = capture
    this.context = context
    this.options = options
    // set when this gets attached to a DOM element
    this._el = null
  }

  // TODO: do we really need this?
  get _isDOMEventListener () { return true }

  static findIndex (eventListeners, eventName, handler) {
    var idx = -1
    if (arguments[1]._isDOMEventListener) {
      idx = eventListeners.indexOf(arguments[1])
    } else {
      idx = findIndex(eventListeners,
        _matches.bind(null, {
          eventName: eventName,
          originalHandler: handler
        })
      )
    }
    return idx
  }
}

function _matches (l1, l2) {
  return l1.eventName === l2.eventName && l1.originalHandler === l2.originalHandler
}

function _once (listener, handler) {
  return function (event) {
    const el = listener._el
    if (el) {
      handler(event)
      el.removeEventListener(listener)
    }
  }
}