We'll use Express in this recipe, however, the particular way Express handles this case represents the norm across frameworks, and indeed the behavior corresponds to Node core functionality.

So let's create a tiny Express app, that shouts back whatever message we give it.

We'll create an app folder, initialize it as a package, install express, and create an index.js file:

$ mkdir app
$ cd app
$ npm init -y
$ npm install --save express
$ touch index.js

Our index.js file should look like the following:

const express = require('express')
const app = express()

app.get('/', (req, res) => {
  pretendDbQuery(() => {
    const yelling = (req.query.msg || '').toUpperCase()
    res.send(yelling)
  })
})

app.listen(3000)

function pretendDbQuery (cb) {
  setTimeout(cb, 0)
}