Working with JSON in Node.js

JSON is the standard data format. Node.js makes it easy.

Parse JSON String

```javascript const jsonString = '{"name": "Alice", "age": 25}'; const obj = JSON.parse(jsonString);

console.log(obj.name); // Alice console.log(obj.age); // 25 ```

Convert to JSON String

```javascript const obj = { name: 'Alice', age: 25 }; const jsonString = JSON.stringify(obj);

console.log(jsonString); // {"name":"Alice","age":25}

// Pretty print const pretty = JSON.stringify(obj, null, 2); console.log(pretty); // { // "name": "Alice", // "age": 25 // } ```

Read JSON File

```javascript const fs = require('fs').promises;

async function readJSON(filepath) { const data = await fs.readFile(filepath, 'utf8'); return JSON.parse(data); }

const config = await readJSON('config.json'); console.log(config); ```

**Simpler with require (for static files):** ```javascript const config = require('./config.json'); // Works but caches the file ```

Write JSON File

```javascript const fs = require('fs').promises;

async function writeJSON(filepath, data) { const json = JSON.stringify(data, null, 2); await fs.writeFile(filepath, json); }

const users = [ { id: 1, name: 'Alice' }, { id: 2, name: 'Bob' } ];

await writeJSON('users.json', users); ```

Update JSON File

```javascript async function updateJSON(filepath, updateFn) { const data = await readJSON(filepath); const updated = updateFn(data); await writeJSON(filepath, updated); }

// Add a user await updateJSON('users.json', users => { users.push({ id: 3, name: 'Charlie' }); return users; }); ```

Handle Errors

```javascript function safeJsonParse(str) { try { return JSON.parse(str); } catch (err) { console.error('Invalid JSON:', err.message); return null; } }

const data = safeJsonParse('invalid json'); // null const valid = safeJsonParse('{"ok": true}'); // {ok: true} ```

Working with API Responses

```javascript const https = require('https');

function fetchJSON(url) { return new Promise((resolve, reject) => { https.get(url, (res) => { let data = ''; res.on('data', chunk => data += chunk); res.on('end', () => resolve(JSON.parse(data))); }).on('error', reject); }); }

const user = await fetchJSON('https://api.github.com/users/octocat'); console.log(user.name); ```

JSON with Dates

```javascript const obj = { name: 'Event', date: new Date() };

const json = JSON.stringify(obj); // {"name":"Event","date":"2024-01-15T10:30:00.000Z"}

// Parse with date conversion const parsed = JSON.parse(json, (key, value) => { if (key === 'date') return new Date(value); return value; }); ```

Practical: Simple JSON Database

```javascript class JsonDB { constructor(filepath) { this.filepath = filepath; } async read() { try { const data = await fs.readFile(this.filepath, 'utf8'); return JSON.parse(data); } catch { return []; } } async write(data) { await fs.writeFile(this.filepath, JSON.stringify(data, null, 2)); } async add(item) { const data = await this.read(); data.push(item); await this.write(data); } }

const db = new JsonDB('data.json'); await db.add({ id: 1, name: 'Item 1' }); ```

Key Takeaway

Use `JSON.parse()` to read JSON strings, `JSON.stringify()` to create them. For files, combine with `fs` module. Always handle parse errors and use pretty printing for readable files.