JavaScript Express / Node : How can I serve different scripts to different customers like Hotjar does?

clientsite.html

<script defer src='https://my.backend.io/v1/library/customer-xyz123/ />

express.js

app.get('/v1/library/:uid', async (req, res) => {
    const customerId = req.params.uid
    const settings = await getSettings(customerId) // { name : 'doug', features: [1, 2 ,5] ... }
    res.sendFile('./libary.js') // How can I take ./library.js as a template, and add customer-xyz123's settings to the script?
}

libary.js

  const settings = { name : 'doug', features: [1, 2 ,5] ... }
  doStuff(settings)