Get headers on page load from node-express app?

I am building an app with node and express and set it up such that when the page loads, some headers are sent to the client. How do I extract that information on the client side? I am using JS/jQuery on the client side. Here's the code in question-

app.get('/', (req, res) => {
  models.game_session.build({
    sid: req.sessionID
  }).save().then((data) => {
    let options = {
      "root": __dirname,
      headers: {
        "x-sid": data.id
      }
    }
    res.sendFile('/index.html', options, (err) => {
      if (err) {
        res.send(err)
      }
    });
  }).catch((e) => {
    res.send(`There was an error`);
  });
});

I am saving the session ID in the database then sending the index file to the client. As you see in the options object, I want to include the session ID in the header to be sent with the index file. How can I retrieve that info on the client side? I'm not sure if I am going about this in the right way- appreciate any help!

via wariofan1