How to convert an object to JSON

Short answer

JSON.stringify() turns an object into a JSON string:

const user = { name: 'Anna', age: 30, admin: false };
 
console.log(JSON.stringify(user));

Output:

{"name":"Anna","age":30,"admin":false}

The third argument sets the indent. That is handy for logs and files:

const user = { name: 'Anna', roles: ['admin'] };
 
console.log(JSON.stringify(user, null, 2));

Output:

{
  "name": "Anna",
  "roles": [
    "admin"
  ]
}

The second argument can be an array of keys to keep:

const user = { name: 'Anna', password: 'secret', email: 'anna@example.com' };
 
console.log(JSON.stringify(user, ['name', 'email']));

Output:

{"name":"Anna","email":"anna@example.com"}

Some values do not survive conversion: functions and undefined disappear, NaN turns into null, and dates become strings:

const data = { a: undefined, b: () => 1, c: NaN, d: new Date(Date.UTC(2025, 0, 1)) };
 
console.log(JSON.stringify(data));

Output:

{"c":null,"d":"2025-01-01T00:00:00.000Z"}