Red Hat developer Stacey Mosier reports that the Javascript example in the RH SSO Securing Apps guide is not printing errors. 

https://access.redhat.com/documentation/en-us/red_hat_single_sign-on/7.6/html/securing_applications_and_services_guide/oidc#javascript_adapter

She suggests it can  be updated to use console.error instead of alert, and print the errors:

keycloak.init(options)
  .then(function(authenticated)

).catch((error) => {
    for (const property in error) {
    console.error(`${property}: ${error[property]}`);
  }
});