src/AdvanceEventEmitterTrait.php
public function on(string $eventName, callable $listener) : self
    {
        $this->listeners[$eventName][] = $listener;

        return $this;
    }
public function on(string $eventName, callable $listener) : self
    {
        $this->listeners[$eventName][] = $listener;

        return $this;
    }
@param string   $eventName
@param callable $listener

@return $this