src/Assets.php
public function getExternalJs($key = null)
    {
        if (isset($this->externalJs[$this->key($key)])) {
            $externalJs = $this->externalJs[$this->key($key)];
            return $this->getJsTags($externalJs);
        }

        return null;
    }
public function getExternalJs($key = null)
    {
        if (isset($this->externalJs[$this->key($key)])) {
            $externalJs = $this->externalJs[$this->key($key)];
            return $this->getJsTags($externalJs);
        }

        return null;
    }
@param null $key

@return string