off (eventName, handler) {
    // el.off(this): disconnect all listeners bound to the given context
    if (arguments.length === 1 && !isString(eventName)) {
      const context = arguments[0]
      this.getEventListeners().filter(function (l) {
        return l.context === context
      }).forEach(function (l) {
        this.removeEventListener(l)
      }.bind(this))
    } else {
      this.removeEventListener(eventName, handler)
    }
    return this
  }
Unregisters the handler of a given event.

    @param {String} event The event name.
    @returns {this}