...
var stripeCharge = require('./stripeCharge.js')

...

app.post('/api/purchase', parseURLencoded, function(req, res) {
  var auth = req.headers['authorization']
  if (auth !== "false") {
    var token = req.body.token
    stripeCharge.charge(token)
    res.status(201)
  } else {
    res.status(401).send("Unauthorized.")
  }
})

...