google-auth is a wrapper library for "Sign in with Google" that simplifies the integration process:

• no need to uglify your html file;
• no untyped global variables;
• framework-agnostic — works with any frontend framework.;
• no hidden properties or any side effects beyond the import;
• includes TypeScript types.

Just type

const google = await GoogleAuth.import();
if (!google) {
    // Google lib loading error
    return;
}

// Proceed with Google Sign-In
google.accounts.id.initialize(...);

and check the Google documentation for further exploration.