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A short description of the issue:

I recently upgraded a project from the Rhino engine to the new V8 engine. When calling:

google.script.run.withSuccessHandler( function() { google.script.host.close(); } ).customFunction(object);

from an HTMLService modal dialogue, the script crashes and the browser's javascript console shows "Uncaught".

No logs appear in the Apps Script editor or Stackdriver.

I added a log message and debug email at the very beginning of the customFunction() but those lines are never executed.

I changed it to call a new, completely blank function instead of customFunction() and the same thing happened - the function is never invoked and the console displays "Uncaught"

The script had previously worked perfectly on Rhino, and this issue only started after upgrading the project to V8. I've reverted back to Rhino and the script works again.

Before upgrading to V8, I ensured that my code should not experience any of the incompatibilities listed here: https://developers.google.com/apps-script/guides/v8-runtime/migration#incompatibilities

A small code sample that reliably reproduces the issue. The sample should run as-is or with minimal setup, without external dependencies.

// template_html:

function onClickFunctions(formData) {

  console.group('onClickFunctions');

  var formValues = '';
  for (var property in formData) { formValues += property + ': ' + formData[property]+'\n'; }
   
  var obj = {};
  obj['testString'] = formData.elements.testString.value;
  obj['testNum'] = Number(formData.elements.testNum.value);
     
  google.script.run.withSuccessHandler( function() { google.script.host.close(); } ).customFunction(obj);

  console.groupEnd();
 
}

// script.gs:

function customFunction() {
 
  Logger.log('starting customFunction');
   
  MailApp.sendEmail('test@test.com', 'test', 'test');
   
}



What steps will reproduce the problem?
1. Call google.script.run.withSuccessHandler( function() { google.script.host.close(); } ).customFunction(obj); from an HTMLService modal.
2. "Uncaught" appears in the browser's javascript console.
3.

What is the expected output? What do you see instead?  If you see error messages, please provide them.

Before upgrading the project to V8, upon calling the server-side customFunction(), the customFunction() would execute without any errors.


Please provide any additional information below.