Node.js — JSON

Parse JSON

const jsonString = '{"name": "John", "age": 30}';
const obj = JSON.parse(jsonString);
console.log(obj.name); // 'John'

Stringify JSON

const obj = { name: 'John', age: 30 };
const jsonString = JSON.stringify(obj);
// '{"name":"John","age":30}'

Pretty Print

const pretty = JSON.stringify(obj, null, 2);

Custom Replacer

const filtered = JSON.stringify(obj, (key, value) => {
    if (key === 'password') return undefined;
    return value;
});

Reading JSON Files

const fs = require('fs');

// Synchronous
const data = JSON.parse(fs.readFileSync('data.json', 'utf8'));

// Asynchronous
const data = JSON.parse(await fs.promises.readFile('data.json', 'utf8'));

Writing JSON Files

const data = { users: [{ name: 'John' }] };
await fs.promises.writeFile('data.json', JSON.stringify(data, null, 2));

Mini Practice

1. Parse JSON strings
2. Stringify objects
3. Read/write JSON files
4. Use custom replacer

Up Next

Continue with REST API — building REST APIs.