How to reliably get session id generated by Google Analytics?

Question

Using the latest analytics.js code (as of today) is there a way through their JS API I can get the session id?

Answer 1

If you're talking about the client ID, you can get that as follows:

ga(function(tracker) {
  var clientId = tracker.get('clientId');
  console.log(clientId);
});

Here's where that's stated in the documentation:
https://developers.google.com/analytics/devguides/collection/analyticsjs/cookies-user-id#getting_the_client_id_from_the_cookie

Keep in mind that the client ID is (usually) stored in a cookie, so if the user clears their cookies, they'll be assigned a new client ID that may not match the one you have.