format json in textarea

json_formatter.js

// preview with hilight.js and pretty json format
$('[name="json_data"]').on('input change', function () {
    let previewWrapper = $(this).siblings('.preview-wrapper');
    const $code = previewWrapper.find('pre > code');
    if ($(this).val()) {      
      try {
        var val = JSON.parse($(this).val())
      } catch (e) {
        $(this).addClass("warning-bordered");
        return false;
      }
      $(this).removeClass("warning-bordered");
      previewWrapper.removeClass("hide");
      $code.text(JSON.stringify(val, undefined, 2))
      hljs.highlightBlock($code[0]);
    } else {
      previewWrapper.addClass("hide");
    }
  })
}