How to Add a New Cell to an Existing Named Range on Google Script

ModifyNamedRange.gs

//This code is developed by Moayad Hani Yacoub Abu Rmilah and can be used freely for whatever purpose

/*This example shows how to:
1- create customized menu on Google Sheet using Google Script
2- Check if a sheet exists using sheet name
3- Get user entry by using UI dialog
4- Add a cell to an existing named range
5- Change text to camel case using regex expressions
6- Showing messages to the user */

//You need to accept the required permissions for this code to work.

var databaseSheetName = 'Database';
var ss = SpreadsheetApp.getActiveSpreadsheet();
var databaseSheet = ss.getSheetByName(databaseSheetName);
var ui = SpreadsheetApp.getUi();
//Create customized menu
function onOpen(e) {
  ui.createMenu('Customized Menu').
  addSubMenu(ui.createMenu('Database:')
             .addItem('New Entry', 'addNewEntry'))
						 .addToUi();
}

function addNewEntry(){
	//return if sheet is missing
  if (isSheetMissing(databaseSheetName)){
    return;
  }
  var myNamedRange = ss.getRange('RangeName1');
  if (!myNamedRange){
    Browser.msgBox('A named range with name "RangeName1" does not exist. It may have been deleted or renamed.');
  }
  var newEntryPrompt = ui.prompt('New Entry', 'Key in a new entry:', Browser.Buttons.OK_CANCEL);
  if (newEntryPrompt.getSelectedButton() == ui.Button.CANCEL){
    return;
  }
  var entryText = newEntryPrompt.getResponseText();
  entryText = toCamelCase(entryText);
  var allEntries = myNamedRange.getValues(); //this is a 2-D array
  var newArr = allEntries.join().split(','); //splits the 2-D array into 1-D array
  if(newArr.indexOf(entryText) != -1){
    Browser.msgBox('Your keyed entry already exists.');
    return;
  }
  
  var firstRow = myNamedRange.getRow();
  var lastRow = myNamedRange.getLastRow();
  var columnNum = myNamedRange.getColumn();
  
  databaseSheet.getRange(lastRow + 1, columnNum).setValue(entryText);
  var newRange = databaseSheet.getRange(firstRow, columnNum, 2 + lastRow - firstRow);
  ss.setNamedRange('RangeName1', newRange);
}

//Check if a sheet is missing (by sheet name)
function isSheetMissing(mySheetName){
  if (!ss.getSheetByName(mySheetName)){
    Browser.msgBox('The sheet named ' + mySheetName + ' does not exist. You may have deleted or renamed the sheet.');
    return true;
  }
}

//Capitalize the first character of each word using regex expressions in string replace
function toCamelCase(str){
  return str.toLowerCase().replace(/\b(.)/g, function($1) { return $1.toUpperCase(); });
}