src/FrontendAsset.php
public function addFirst($file, $params = 'footer', $onUnknownExtension = false)
    {
        RoumenAsset::addFirst($this->elixir($file), $params, $onUnknownExtension);
    }
public function addFirst($file, $params = 'footer', $onUnknownExtension = false)
    {
        RoumenAsset::addFirst($this->elixir($file), $params, $onUnknownExtension);
    }
Add the asset first using our version of the exliser loader.

@param string $file
@param string $params
@param bool   $onUnknownExtension

@return return string