How do you read and write files in Node.js?

Direct answer

Use fs.promises.readFile/writeFile for async Promise-based I/O, or fs.createReadStream for large files — avoid readFileSync on servers; handle errors with try/catch and validate paths.

The fs module wraps libuv file operations (Q8–10). Promises API fits async/await handlers; streams fit large JSON imports like AceDevHub interview content files.

API	Style	When
fs.promises.readFile	Async Promise	Small/medium files, JSON config
fs.readFile + callback	Async callback	Legacy codebases
fs.readFileSync	Blocking sync	CLI scripts at startup only
fs.createReadStream	Stream	Large files, line-by-line parsing
fs.promises.writeFile	Async Promise	Save output, generate files

Encoding — 'utf8' returns string; omit encoding for Buffer binary.
JSON.parse — wrap readFile + parse in try/catch; invalid JSON throws.
Permissions — EACCES and ENOENT need user-friendly errors; do not leak paths in public API.

fs-read-write.mjs

import fs from "node:fs/promises";
import path from "node:path";

async function loadInterviewJson(relativePath) {
  const fullPath = path.resolve(relativePath);
  const raw = await fs.readFile(fullPath, "utf8");
  return JSON.parse(raw);
}

async function saveReport(dir, filename, data) {
  await fs.mkdir(dir, { recursive: true });
  await fs.writeFile(
    path.join(dir, filename),
    JSON.stringify(data, null, 2),
    "utf8"
  );
}