Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
/**
  * Preloads information template into summary field of file ulpads
  * and adds preview functionality to [[Special:Upload]]
  * 
  * Code by [[de:Benutzer:Schnark]] on German Wikipedia
  * Ported to English Wikipedia by [[User:Patrick87]]
  * <nowiki>
  */
 mw.loader.using(['mediawiki.util'], function() { $(function() {
  var $editbox = $('#wpUploadDescription');
  if ($editbox.length != 1) return; // exits silently if not exactly one #wpUploadDescription is found
  var parseAsSummary; // distinguish between new upload and reupload for preview function
  if (mw.util.getParamValue('wpForReUpload') != '1') { // upload of new file (e.g. no reupload)?
     parseAsSummary = false; // upload description will be displayed on file page for new uploads

     if (typeof wikEd != 'undefined' && wikEd.useWikEd) {  // if WikEd is active
        wikEd.UpdateTextarea(); // transfer WikEd to $editbox
     }

     if ($editbox.val() === '') {
        $editbox.val('{{Information\n' +
                     '| description    = \n' +
                     '| source         = \n' +
                     '| date           = \n' +
                     '| author         = \n' +
                     '| permission     = \n' +
                     '| other_versions = \n' +
                     '| additional_information = \n' +
                     '}}');
     }

     if (typeof wikEd != 'undefined' && wikEd.useWikEd) {  // if WikEd is active
        wikEd.UpdateFrame(); // transfer $editbox to WikEd
     }
  } else {
     parseAsSummary = true; // upload description will only be displayed in file log for uploads of new file version
  }

  if (false) return;
  var previewText = 'Preview';
  if ($('#mw-description-preview').length === 0) {
     $('#mw-htmlform-description').before($(mw.html.element('div', {id: 'mw-description-preview'})));
  }
  $('input[name="wpUpload"]').after($(mw.html.element('input', {value: previewText, type: 'button', id: 'wpPreview', title: previewText + ' [p]', accesskey: 'p'})).click(function(){
    if (typeof wikEd != 'undefined'&& wikEd.useWikEd) {  // if WikEd is active
       wikEd.UpdateTextarea(); // transfer WikEd to $editbox
    }
    var param = {action: 'parse',
                 title: 'File:' + ($('#wpDestFile').val() || 'Example.jpg'), // title, File:Example.jpg as default
                 prop: 'text',
                 pst: '',
                 text: '', // empty text field necessary even when parsed as summary, see bug 48319
                 format: 'json'};
    param[ parseAsSummary ? 'summary' : 'text' ] = $editbox.val(); // use upload description either as summary or as page text
    $.getJSON(mw.util.wikiScript('api'), param, function (json) {
       var content = parseAsSummary ? 'parsedsummary' : 'text'; // set type of content to either parsedsummary or text
       if (!json || !json.parse || !json.parse[content] || !json.parse[content]['*']) return;
       var html = '<p><strong>' + previewText + ':</strong><p>' + json.parse[content]['*'];
       $('#mw-description-preview').html(html);
    }); //getJSON
  })); //click
  $('#t-print a').removeAttr('accesskey'); // T58786
  $('#t-print a, #wpPreview').updateTooltipAccessKeys();
 });}); //ready
//</nowiki>