How do you work with JSON in Node.js?

Direct answer

Use JSON.parse for strings and JSON.stringify for objects — read/write JSON files with fs and validate shape before use; handle parse errors and avoid circular references when stringifying.

JSON is the default wire format for REST APIs and config files. Node exposes JSON globally — no import needed — but parsing untrusted input still requires validation.

Why interviewers ask

API handlers — every POST/PUT body and JSON response path uses parse/stringify.
Config & content — package.json, interview import JSON, .env is not JSON but often paired with JSON config.
Failure modes — invalid JSON, BigInt, Date, undefined in objects, circular graphs.

Method	Use case
JSON.parse(str)	String → object; throws SyntaxError on bad input
JSON.stringify(obj)	Object → string; replacer/space for pretty print
fs + parse	Load local JSON files (content import, fixtures)
res.end(JSON.stringify(...))	Raw http JSON response

json-handling.mjs

function safeParseJson(raw) {
  try {
    return { ok: true, data: JSON.parse(raw) };
  } catch (err) {
    return { ok: false, error: err.message };
  }
}

const payload = { topic: "nodejs-interview-questions", count: 30 };
const json = JSON.stringify(payload, null, 2);

// BigInt and undefined are not JSON-safe by default
// JSON.stringify({ n: 1n }) throws