How to check if user is logged in or not with “Google Sign In” (OAuth 2.0)

Question

I am implementing Google log in for the first time as described here and here.

I am using HTML with Javascript.

The problem that needs solving is as follows:

Answer 1

Adding on to Joseph's answer above, you can then get information about the user by calling auth2.currentUser.get().getBasicProfile().

    if (auth2.isSignedIn.get()) {
        googleUserProfile = auth2.currentUser.get().getBasicProfile()
        console.log('ID: ' + googleUserProfile.getId());
        console.log('Full Name: ' + googleUserProfile.getName());
        console.log('Given Name: ' + googleUserProfile.getGivenName());
        console.log('Family Name: ' + googleUserProfile.getFamilyName());
        console.log('Image URL: ' + googleUserProfile.getImageUrl());
        console.log('Email: ' + googleUserProfile.getEmail());
    }

From the docs: https://developers.google.com/identity/sign-in/web/people