Cheat sheet · Back end and data
Node.js cheat sheet
Run scripts, use modules, read files, build a small server and manage packages with npm.
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- Back end and data
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Cheat sheet
Node.js
Run scripts, use modules, read files, build a small server and manage packages with npm.
Run and packages
node app.js- Run a file
npm init -y- Create package.json
npm install <name>- Add a package
npm install -D <name>- Add a package used only while developing
npm run <script>- Run a script from package.json
npx <tool>- Run a package without installing it
Modules
import fs from "node:fs"- Import (ES modules; set "type": "module")
export default fn / export { a, b }- Share things from a file
const x = require("x")- The older CommonJS way
import.meta.url- Address of the current file (ES modules)
Files and paths
await fs.promises.readFile(p, "utf8")- Read a file as text
await fs.promises.writeFile(p, text)- Write a file
await fs.promises.readdir(dir)- List a folder
path.join(a, b)- Join path parts safely
path.extname("a.txt")- ".txt"
Process and environment
process.env.PORT- Read an environment variable
process.argv- Command-line arguments
process.exit(1)- Stop with an error code
process.on("unhandledRejection", fn)- Catch promises nobody handled
A small server
http.createServer((req, res) => { })- Handle each request
res.writeHead(200, { "Content-Type": "text/plain" })- Set status and headers
res.end("Hello")- Send the body and finish
server.listen(3000)- Start listening on a port
Events and streams
emitter.on("event", fn)- Listen for an event
emitter.emit("event", data)- Fire the event
fs.createReadStream(p).pipe(res)- Send a big file in small pieces
Remember
- Never block the main thread with a long loop. Use async functions for files and network.
- Keep secrets in environment variables, and never commit a .env file.
Learn it properly
A cheat sheet helps you remember. These lessons explain the ideas step by step, with examples.