Symfony knp_snappy bundle: Execute JS in the twig template to be printed as PDF

Question

I'm trying to print the PDF using knp_snappy bundle. Every thing seems to be working seamlessly except for the JS. The twig template it self contains a form with a large number of input fields. I need to execute JS to hide the labels for the input fields which are empty before generating the PDF. Prior to printing, empty input fields are not known.Here's what I have tried so far:

        $reportHTML = $this->render('template.html.twig', array());

        $options = array(
            'enable-javascript' => true,
            'javascript-delay' => 1000,
            'no-outline' => true,
            'image-dpi'     => 600,
            'image-quality' => 100,
            'margin-top' => 2,
            'margin-right' => 0,
            'margin-bottom' => 5,
            'margin-left' => 0,
            'page-width' => '22cm',
            'page-height' => '36cm',
        );

        $snappyPdf = $this->get('knp_snappy.pdf');
        $snappyPdf->setOptions($options);
        $snappyPdf->setOption('enable-local-file-access', true);
        return new PdfResponse(
            $snappyPdf->getOutputFromHtml($reportHTML),
            "contract.pdf"
        );