JSON format

JSON is a subset of JavaScript, JavaScript is built upon JSON
Data format

Valid JavaScript:

const user = {
  firstname: 'Lucky',
  lastname: `Luke`,
  "password": "secret",
  age: 42,
  mood: 0.9,
  languages: ['en', ['fr_FR', 'fr_CA'] , , ],
  level: null,
  friends: undefined,
};

Valid JSON:

{
  "firstname": "Lucky",
  "lastname": "Luke",
  "password": "secret",
  "age": 42,
  "mood": 0.9,
  "languages": ["en", ["fr_FR", "fr_CA"]],
  "level": null
}