code: function shareEvent(eventName, source, target, once = false) {
    verifyEventEmitter(source, 'source')
    verifyEventEmitter(target, 'target')
  
    const cb = target.emit.bind(target, eventName)
  
    source[once ? 'once' : 'on'](eventName, cb)
  
    return cb
  }
docs: Share an event from the source with the target.
  @param {string} eventName - The name of the event.
  @param {*} source - The EventEmitter that emits the event.
  @param {*} target - The EventEmitter that should also emit the event.
  @param {boolean} [once] - Share the event only once.
  @returns {function} - The callback that has been applied to the target.