client.ts

// This would be the client in the npm package
export const plausible: (arg: 'page' | 'trackPushState') => void = (window['plausible'] =
  window['plausible'] ||
  function(
    ...args: any[] // eslint-disable-line
  ) {
    ;(window['plausible'].q = window['plausible'].q || []).push(args)
  })
const js = document.createElement('script')
js.id = 'plausible'
js.src = '/plausible/js/p.js' // the path might need to be configurable
js.async = true
document.head.appendChild(js)

server.ts

import proxy from 'http-proxy-middleware'

// proxy to plausible
app.use( // app is an express app
  '/plausible',
  proxy({
    target: 'https://plausible.io',
    pathRewrite: { '^/plausible': '' },
  })
)