Add a timestamp to a cell in Google Sheets (Gsheets)

timestamp_sheet.js

function addTimestamp(){
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var cell = sheet.getRange('A1');
  var d = new Date();
  d.setHours(d.getHours());
  var user = Session.getActiveUser().getUserLoginId();
  user = String(user);
  // cosmetic: this just removes the email domain from the user info
  user = user.replace('@gmail.com', '');
  cell.setValue('Last updated: ' + d.toLocaleString() + ' by ' + user);
}