Getting no response when sending GET request from localhost:3000 to localhost:8000

client.js

// currently running on localhost:3000
const xhr = new XMLHttpRequest()
const url = 'localhost:8000/'
xhr.open('GET', url)
xhr.onreadystatechange = function() {
  console.log(xhr.responseText) // logs nothing
}
xhr.send()

server.js

const express = require('express')
const cors = require('cors')

const app = express()
const port = 8000

app.use(cors())

app.get('/', (req, res) => {
  console.log('got a get request') // never logs
  res.send('ok')
})

app.listen(port, () => console.log(`Example app listening on port ${port}!`))