Google apps script to add header numbers to a document

AddHeaderNumbers.js

var state = {
  headerLevel1: 0,
  headerLevel2: 0,
  headerLevel3: 0,
}
 
var private = {
  getSectionNumber: function (paragraph)
  {
    if ( paragraph.getHeading() == DocumentApp.ParagraphHeading.HEADING1 )
    {
      state.headerLevel2 = 0;
      state.headerLevel3 = 0;
      
      return (++state.headerLevel1) + " ";
    }
    else if ( paragraph.getHeading() == DocumentApp.ParagraphHeading.HEADING2 )
    {
      if (state.headerLevel1 == 0)
        state.headerLevel1 = 1;
      
      state.headerLevel3 = 0;
      
      return state.headerLevel1 + "." + (++state.headerLevel2) + " ";
    }
    else if ( paragraph.getHeading() == DocumentApp.ParagraphHeading.HEADING3 )
    {
      if (state.headerLevel2 == 0)
        state.headerLevel2 = 1;
      
      return state.headerLevel1 + "." + state.headerLevel2 + "." + (++state.headerLevel3) + " ";
    }
    
    return "";
  },
  
  isNumber: function (text)
  {
    return !isNaN(text);
  },
 
  removeExistingHeaderNumber: function (paragraph)
  {
    var text = paragraph.getText();
    
    for (var i = 0; i < text.length; i++)
    {
      if ( private.isNumber(text.charAt(i)) || text.charAt(i) == "." )
          continue;
      
      break;
    }
    
    return text.substr(0, i);
  }
};

var _addHeaderNumbers =
{
  testUrl: "xyzzy",
  
  implHelper : function addHeaderNumbers(doc) 
  {
    var body = doc.getBody()
    
    for (var i = 0; i < body.getNumChildren(); i++)
    {
      var element = body.getChild(i);
      
      if ( element.getType() != DocumentApp.ElementType.PARAGRAPH )
        continue;
      
      var paragraph = element.asParagraph();
      
      if ( paragraph.getHeading() != DocumentApp.ParagraphHeading.NORMAL )
      {
        var sectionNumber = private.getSectionNumber(paragraph);
        
        var oldText = private.removeExistingHeaderNumber(paragraph);
        if ( oldText.length > 0 )
          paragraph.replaceText(oldText, "");
        
        if ( sectionNumber.length > 0 )
          paragraph.insertText(0, sectionNumber);
      }
    }
    
    doc.saveAndClose();
  }
  
};

function _test_addHeaderNumber()
{
  _addHeaderNumbers.implHelper(DocumentApp.openByUrl(_addHeaderNumbers.testUrl));
}

function addHeaderNumbers() 
{
  _addHeaderNumbers.implHelper(DocumentApp.getActiveDocument());
}