HTML form is not running a (withSuccessHandler)fun

I have this HTML form in Google App Script(Sheets) that asks a user for a date value and then to submit the value. The HTML form runs. the only problem is the obj doesn't log. I can't figure out why this is.

The HTML:

<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
  </head>
  <body>
   <form id="myForm">

    <input type="date" name="startDate" value="" id="demo" >
    <input type="button" style="font-family: verdana;" value="Submit" onclick="getStartDate()">

   </form> 
    <script>
  function success(msg) {
    alert(msg);
  }

  function getStartDate(){
    var form = document.getElementById("myForm").elements;
    var obj ={};
    for(var i = 0 ; i < form.length ; i++){
        var item = form.item(i);
        obj[item.name] = item.value;
    }
    google.script.run
    .withSuccessHandler(success)
    .getStartDate(obj);

    google.script.host.close();
  };
  </script>
  </body>
</html>

The Javascript:

function getStartDate(obj){
  Logger.log(obj)
}

This should output the object but it doesn't.

Thanks for your help!

How about this modification?

Modification points:

google.script.run works by the asynchronous processing. So in your script, getStartDate() and success() are not run due to google.script.host.close().
getStartDate() at GAS side doesn't return values. So alert(msg) shows undefined.

When above points are reflected to your script, it becomes as follows.

Modified script:

HTML:

Please modify Javascript as follows.

function success(msg) {
  alert(JSON.stringify(msg)); // Modified
}

function getStartDate(){
  var form = document.getElementById("myForm").elements;
  var obj ={};
  for(var i = 0 ; i < form.length ; i++){
    var item = form.item(i);
    obj[item.name] = item.value;
  }
  google.script.run
  .withSuccessHandler(function(e) { // Modified
    success(e);
    google.script.host.close();
  })
  .getStartDate(obj);
};

GAS:

function getStartDate(obj){
  Logger.log(obj)
  return obj; // Modified
}

Note:

If you want to give the key to Submit, please add name to <input type="button" style="font-family: verdana;" value="Submit" onclick="getStartDate()">.
Of course, you can also move google.script.host.close() to success().