sakura/resources/views/yuuno/settings/appearance/_preview.twig

<script type="text/javascript">
    var parser = new Sakura.AJAX(),
        textMax = {{ maxLength }},
        form = document.getElementById("settingsEditor"),
        preview = document.getElementById("settingsPreview");

    parser.SetUrl("{{ route('helper.bbcode.parse') }}");
    parser.ContentType("application/x-www-form-urlencoded");

    function settingsPreview() {
        var text = form.value;

        if (text.length == 0) {
            preview.innerHTML = "";
        } else if (text.length > textMax) {
            preview.innerHTML = "<span style='color: red;'>Too long!</span>";
        } else {
            parser.SetSend({"text":text});

            parser.AddCallback(200, function () {
                preview.innerHTML = parser.Response();

                var codeBlocks = preview.querySelectorAll("pre code");

                for (var _i in codeBlocks) {
                    if ((typeof codeBlocks[_i]).toLowerCase() === 'object') {
                        hljs.highlightBlock(codeBlocks[_i]);
                    }
                }
            });

            parser.Start(Sakura.HTTPMethod.POST);
        }
    }
</script>