Auto generate sorta unique IDs for each row in Google Sheets

code.gs

// This script fires when any cell is edited and the corresponding ID cell
// on the same row is empty. It will insert a reasonably unique UID of ID_length
// into the specified ID cell under the ID column.
// replace this with your sheet name
var ID_length = 5;
var targetSheet = 'Tasks';
// The header name of the column that stores unique IDs
var idHeader = 'Task ID';

// This function will get all the header names of the specified data range
// and their corresponding column number.
function getHeaderColumns(sheetName, startValue) {
  var ss = SpreadsheetApp.getActiveSpreadSheet();
  var sheet = ss.getSheetByName(sheetName);
  // Return a range bounded by cell A1 and the last row and last column with content
  // The range can be a single cell, or a rectangle of multiple rows and multiple
  // columns, like B3:N75
  var allData = ss.getDataRange().getValues();
  var obj = {};
  // Loop through each row of the range. The loop starts from 1 because row 1 in the
  // spreadsheet are used as page margin
  Loop1: for (var i = 1; i < allData.length; i++) {
    var curRow = allData[i];
    // Loop through each column. The inner loop also starts from 1 because column A
    // are used as page margin
    Loop2: for (var j = 1; j < curRow.length; j++) {
      // The startValue variable refers to the value in the top left cell of the range.
      // Because Google Sheets works like a sandbox, there may be data in the sheets
      // that don't belong to a table. This double looping provides a failsafe mechanism
      // account for that case.
       if (curRow[j] === startValue) {
         // Save the row number of the table header. It is 1 value larger than i because
         // rows in Google Sheets start at 1, while standard Javascript arrays use zero-
         //-based indexing.
         obj['row'] = i + 1;
         obj[['col'] = j + 1;
         obj['cols'] = {};
         curRow.forEach(function(elem, index) {
          obj['cols'][elem] = index + 1;
         })
         break Loop1
       }
    }
  }
  // Example of obj: [{'row': 3, 'col': 2, cols: {'Status': 2, 'Task Name': 3, 'Task ID': 4}}
  return obj;
}

function onEdit(e) {
  var ss = e.source.getActiveSheet();
  var sName = ss.getName();
  if (sheet !== targetSheet) return;
  var headerObj = getHeaderColumn(sName, 'Status');
  var thisRow = e.range.getRow();
  var idCol = headerObj[idHeader];
  var idCell = ss.getRange(thisRow, idCol);
  // ONly generate unique ID if the ID cell is blank
  if (idCell.isBlank()) {
    idCell.setValue(generateUID());
  }
}