Core Modules: fs, path, http and os

• Core modules ship with Node: no install
• Import with the node: prefix to show they are built in
• import fs from 'node:fs'

• Callback: err is always the first argument
• Sync: wrap in try/catch

import fs from 'node:fs';
import { readFile } from 'node:fs/promises';
fs.readFile('a.txt', 'utf8', (err, data) => {});
const text = await readFile('a.txt', 'utf8');
try { fs.readFileSync('a.txt', 'utf8'); } catch (e) {}

callback, promise, sync

• Preferred: fs/promises + await inside try/catch
• Import: import { readFile, writeFile } from 'node:fs/promises'

• join concatenates segments and normalizes separators and ..
• The result of join can stay relative
• resolve builds an absolute path, processing right to left until absolute
• If no segment is absolute, it falls back to process.cwd()

• http.createServer(cb) returns a server; cb runs once per request
• server.listen(port) starts it
• req: readable stream with req.method, req.url, req.headers
• res: ==writable stream**

• os.cpus().length cores; os.totalmem() and os.freemem() in bytes
• os.platform() gives linux, win32 or darwin
• os.homedir(), os.tmpdir(), os.EOL (line ending)