How do I know a gmail account is a member of Google Groups?

is Open Shared File By Prop.gs

// Can I open shared file in a group?
function isOpenSharedFileByProp_() {
  // https://developers.google.com/apps-script/reference/properties/properties-service#getScriptProperties()
  var ss, ssIdsharedGfolderCopy;
  ssIdsharedGfolderCopy = PropertiesService.getScriptProperties().getProperty('ssIdsharedGfolderCopy');
  // Logger.log(ssIdsharedGfolderCopy);
  try {
    ss = SpreadsheetApp.openById(ssIdsharedGfolderCopy);
    return ss ? true: false;
  } catch(e) {
    return false;
  }  
}

function t_isOpenSharedFileByProp() {
  var bool = isOpenSharedFileByProp_();
  Logger.log('return: %s', bool);
}

How do I know a gmail account is a member of Google Groups?

https://stackoverflow.com/questions/48240641/how-do-i-know-a-gmail-account-is-a-member-of-google-groups

I am creating a web app with Google Apps Script. I want to know if an app user is a member of Google Groups.

Group site: https://groups.google.com/

It is not groups managed by G suite.

Create a Google spreadsheet. Open this and add the group's email in the sharing task.

When I open a file shared by a group in a script and open it, can I verify that it is a member of the group?

google-apps-script, google-groups