How to build the add project tag (from Preferences)

TaskPaper
3

Here is the script translated into Javascript (automatically, so code is a bit messy, but functional) and wrapped in script that will run from Script Editor app:

var TaskPaper = Application('TaskPaper')

function TaskPaperContext(editor, options) {
  let outline = editor.outline;
  let selection = editor.selection;
  let startItem = selection.startItem;
  let endItem = selection.endItem;
  let archive = outline.evaluateItemPath("//@text = Archive:")[0];
  let doneItems = Item.getCommonAncestors(outline.evaluateItemPath("//@done except //@text = Archive://@done"));
  let removeExtraTags = Birch.preferences.get('BRemoveExtraTagsWhenArchivingDone');
  let addProjectTag = Birch.preferences.get('BIncludeProjectWhenArchivingDone');
  
  outline.groupUndoAndChanges(() => {
    var each, eachName, eachProject, i, j, len, len1, previousItem, projects, ref;
    if (!archive) {
      outline.root.appendChildren(archive = outline.createItem('Archive:'));
    }
	
    for (i = 0, len = doneItems.length; i < len; i++) {
      each = doneItems[i];
      if (removeExtraTags) {
        ref = each.attributeNames;
        for (j = 0, len1 = ref.length; j < len1; j++) {
          eachName = ref[j];
          if (eachName.indexOf('data-') === 0 && eachName !== 'data-type' && eachName !== 'data-done') {
            each.removeAttribute(eachName);
          }
        }
      }
	  
      if (addProjectTag) {
        if (projects = ((function() {
          var k, len2, ref1, results;
          ref1 = outline.evaluateItemPath('ancestor::@type=project', each);
          results = [];
          for (k = 0, len2 = ref1.length; k < len2; k++) {
            eachProject = ref1[k];
            results.push(eachProject.bodyContentString);
          }
          return results;
        })()).join(' / ')) {
          each.setAttribute('data-project', projects);
        }
      }
	  
      if ((each === startItem || each.contains(startItem)) || (each === endItem || each.contains(endItem))) {
        if (previousItem = editor.getPreviousDisplayedItem(startItem)) {
          selection = {
            startItem: previousItem,
            startOffset: -1
          };
        } else {
          selection = {
            start: 0
          };
        }
      }
    }
    return archive.insertChildrenBefore(doneItems, archive.firstChild);
  });
  
  return editor.moveSelectionToItems(selection);
}

var text = TaskPaper.documents[0].evaluate({
	script: TaskPaperContext.toString()
});

TaskPaper.includeStandardAdditions = true
TaskPaper.setTheClipboardTo(text)