google apps script to read spreadsheet

spreadsheet_read_test.gs

function readSheet(){
  var data = openSheet().getDataRange().getValues();
  return data;
}

function doGet() {
  const htmlOutput = HtmlService.createTemplateFromFile('ss_open_test').evaluate();
  htmlOutput.setTitle("スプレッドシート読み込みテスト");
  return htmlOutput;
}

function openSheet() {
  var id = "1lDnkZwZxwB0DCN5FtKQJvE44y-LIu9_vsviz9Yn-j7s";
  var ss = SpreadsheetApp.openById(id).getSheetByName("messages");
  return ss;
}