function doGet() {
    return HtmlService.createTemplateFromFile("index.html")
    .evaluate()
    .setSandboxMode(HtmlService.SandboxMode.IFRAME);
}

function include(filename) {
  return HtmlService.createHtmlOutputFromFile(filename)
      .setSandboxMode(HtmlService.SandboxMode.IFRAME)
      .getContent();
}

function getData(){
  var sheetid = "your sheet id";
  var sheet = SpreadsheetApp.openById(sheetid).getSheets()[0];
  return sheet.getDataRange().getValues();
}