Apps Script to Generate a table of contents in Docs

function generateTableOfContents() {
  const doc = DocumentApp.getActiveDocument();
  const body = doc.getBody();

  // Create a new list for the Table of Contents
  const toc = body.insertParagraph(0, 'Table of Contents');
  toc.setHeading(DocumentApp.ParagraphHeading.HEADING1);

  // Add a line break after the ToC title
  body.insertParagraph(1, '');

  // Keep track of the position to insert the ToC entries
  let tocIndex = 2;

  // Iterate over all paragraphs to find those with Heading 1
  const paragraphs = body.getParagraphs();
  paragraphs.forEach((paragraph) => {
    if (paragraph.getHeading() === DocumentApp.ParagraphHeading.HEADING1) {
      // Use the text of the Heading 1 as the ToC entry
      const text = paragraph.getText();
      const tocEntry = body.insertParagraph(tocIndex, text);

      // Make the ToC entry a hyperlink that jumps to the Heading 1 position
      const position = doc.newPosition(paragraph, 0);
      const bookmark = doc.addBookmark(position);
      tocEntry.setLinkUrl('#' + bookmark.getId());

      // Increment the position for the next ToC entry
      tocIndex++;
    }
  });

  // Finally, add a visual separator after the ToC
  if (tocIndex > 2) { // Ensure there's at least one entry in the ToC
    body.insertParagraph(tocIndex, '-----').setAlignment(DocumentApp.HorizontalAlignment.CENTER);
  }
}