Experiment to create a document map for Google Docs using Google Apps Script

gistfile1.js

function onOpen() {
  // Add a menu with some items, some separators, and a sub-menu.
  DocumentApp.getUi().createMenu('Custom')
      .addItem('Show Document Map', 'showDocumentMap')
      .addToUi();
}


function showDocumentMap() {
// based on http://stackoverflow.com/a/12244248/1027723
  var docmap = {};
  var tocDat = {};
  var doc = DocumentApp.getActiveDocument(); //get active document
  for (var i = 0; i < doc.getNumChildren(); i++) { // loop all the document elements
    var p = doc.getChild(i);
    if (p.getType() == DocumentApp.ElementType.TABLE_OF_CONTENTS) { // if the element type is a TABLE_OF_CONTENTS extract item links
      var toc = p.asTableOfContents();
      for (var ti = 0; ti < toc.getNumChildren(); ti++) { // looping over each ToC item
        var itemToc = toc.getChild(ti).asParagraph().getChild(0).asText();
        var itemText = itemToc.getText();
        var itemUrl = itemToc.getLinkUrl();
        tocDat[itemText] = itemUrl; // create object array
      }
    }
    
    // Doesn't appear to be any section level data in ToC so get this manually by going through document    
    if (p.getType() == DocumentApp.ElementType.PARAGRAPH){ // only need to get paragraphs
      var heading = doc.getChild(i).asParagraph().getHeading();
      var title = doc.getChild(i).asParagraph().asText().getText();
      // if a heading map heading text to heading level
      if (heading == DocumentApp.ParagraphHeading.HEADING1){
        docmap[title] = 1;
      } else if (heading == DocumentApp.ParagraphHeading.HEADING2){
        docmap[title] = 2;
      } else if (heading == DocumentApp.ParagraphHeading.HEADING3){
        docmap[title] = 3;
      } else if (heading == DocumentApp.ParagraphHeading.HEADING4){
        docmap[title] = 4;
      } else if (heading == DocumentApp.ParagraphHeading.HEADING5){
        docmap[title] = 5;
      } else if (heading == DocumentApp.ParagraphHeading.HEADING6){
        docmap[title] = 6;
      } 
    }
  }
  
  // build some html to render in sidebar (you can also use UIInstance for this)
  var html = "";
  var last_level = 0
  
  for (i in docmap){
    var level = docmap[i];
    // not sure if this entirely works (basically want to nest subsections) 
    if(level > last_level)
        html += "<ul>";
    else if (level < last_level){
        html += "</ul>";
    }
    html +=  Utilities.formatString("<li><a href='%s'>%s</a></li>", tocDat[i],i);
    last_level = level;
  }
  html += "</ul>"; //close unorder list
  html += "<p align='right'><a href='http://mashe.hawksey.info/'>MASHe blog</a></p>"; // add link to see if these actually render 
  
  // push out to sidebar
  DocumentApp.getUi().showSidebar(
      HtmlService
          .createHtmlOutput(html)
          .setTitle('Document Map')
          .setWidth(250));
}

Thank you, this script seems to be useful!
The only problem is that the code doesn't work nowadays. When running it I get an error message "Error: Not enough arguments (row 59, file Code)". Could you fix it?