Node.js Foundations·From script to service

The runtime and modules

Node runs JavaScript outside the browser and gives it files, processes and modules.

Intermediate 12 min read Lesson 6 of 300 Challenge included

What you will be able to do

Use import and export with "type": "module" in package.json.
Read configuration from environment variables, never hard-code secrets.
Keep startup code separate from testable module code.

In plain English

Node uses an event loop and non-blocking I/O. ES modules are the modern default. The package.json file records dependencies and scripts; the engines field documents the runtime you support.

server.mjsJavaScript

import { createServer } from 'node:http'

const port = Number(process.env.PORT || 3000)

const server = createServer((request, response) => {
  response.writeHead(200, { 'content-type': 'application/json' })
  response.end(JSON.stringify({ ok: true, path: request.url }))
})

server.listen(port, () => {
  console.log('Listening on ' + port)
})

Your turn

Read a port safely

Easy

Read PORT from the environment and fall back to 3000. Print the value as a number.

JS · starter

const port = process.env.PORT

Check your understanding before moving on.

Knowledge checkQuestion 1

What does the engines field in package.json communicate?

Select an answer to continue

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Next: A JSON HTTP API

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