Move Sheet to Last Tab

move_sheet.google.js

function move_sheet () {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheets_number = spreadsheet.getNumSheets();
    // https://developers.google.com/apps-script/reference/spreadsheet/spreadsheet#getnumsheets
  spreadsheet.moveActiveSheet(sheets_number);
    // https://developers.google.com/apps-script/reference/spreadsheet/spreadsheet#moveActiveSheet(Integer)
}