Why is variable from one js file getting undefined when sent to another js file

Currently, I have this code block which is the back-end for my Stripe setup. On the callback function, I'm setting a variable equal to the amount that gets charged to the user's card. I then want to send this value into another route file so that I can res.send() the amount into the browser.

When I try to do this, the variable somehow gets set to undefined from point a to point b.

router.post('/charge', function(req, res, next) {
    var token = req.body.stripeToken;
    var chargeAmount = req.body.amount[0];
    var charge = stripe.charges.create({
      amount: chargeAmount,
      currency: "usd",
      source: token
    }, function(err, charge) {
      if(err) {
        return console.log(err);
      }
      module.exports.theAmount = charge.amount;
      res.redirect('/users/dashboard');
    });
});

module.exports = router;

Here's the code from the route file that I'm trying to get the charge amount into:

var stripeFile = require('stripe');

router.get('/dashboard', isLoggedIn, function(req, res, next) {
  var messages = req.flash('error');
  res.render('users/dashboard', {messages: messages, hasErrors: messages.length > 0});
  console.log(stripeFile.theAmount);
});

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