GAS issue

code.gs

function onOpen() {

  
  var ui = SpreadsheetApp.getUi();
  
  var utilities = ui.createMenu('Utilities');
  utilities
  .addItem('Open', 'openDialog')
  .addToUi();
}

function openDialog() {
  var template = HtmlService.createHtmlOutputFromFile('index');
  SpreadsheetApp.getUi().showModalDialog(template, 'Dialog');
}

function doGet() {
  return HtmlService.createHtmlOutputFromFile('index');
}

function doSomething() {
  Logger.log('Received object');
}

index.html

<script>
    google.script.run.doSomething();
</script>