In Laravel the main app template has the following line
<script>window.Laravel = <?php echo json_encode(['csrfToken' => csrf_token(),]); ?></script>
<script>window.Laravel = {{ data|json_encode(['csrfToken': csrf_token(),]) }}</script>
<script>window.Laravel = {{ data|json_encode(['csrfToken' => csrf_token(),]) }}</script>
Correct format should be:
<script>window.Laravel = {{ {'csrfToken': csrf_token()}|json_encode()|raw }}</script>
See for more info: http://twig.sensiolabs.org/doc/filters/json_encode.html