gistfile1.js

function onSignIn(authResult) {
  if (!authResult.status.signed_in) {
    gapi.signin.render('signinbutton');
  } else {
    if (authResult.scope.indexOf(YOUTUBE_SCOPE) != -1) {
      log("User has YouTube scope");
    }

    token = gapi.auth.unsafeUnpackIdToken(authResult);
    if (lastUser === undefined) {
      lastUser = token.sub;
    } else if(token.sub != lastUser) {
      log("User has chosen a page!");
      // Our YouTube user is a different user, so we can take 
      // appropriate action - for example sending a code to the
      // server and indicating this should be stored separately.
      //...
    }
  }
  console.log(authResult);
}