JavaScript JSON

What is JSON?

JSON (JavaScript Object Notation) is the standard text format for exchanging data between servers and apps. It looks like JavaScript objects, with stricter rules: keys must be double-quoted strings, and values can only be strings, numbers, booleans, null, arrays and objects.

JSON.stringify — object to text

const user = { name: "Ada", skills: ["js", "sql"], active: true, greet() {} };
const text = JSON.stringify(user);
console.log(text);
console.log(typeof text);
console.log(JSON.stringify({ id: 1, tags: ["a"] }, null, 2));

{"name":"Ada","skills":["js","sql"],"active":true}
string
{
  "id": 1,
  "tags": [
    "a"
  ]
}

The third argument pretty-prints with indentation. Functions and undefined values are skipped.

JSON.parse — text to object

const response = '{"id": 42, "title": "Learn JSON", "done": false}';
const todo = JSON.parse(response);
console.log(todo.title, todo.done);
try {
  JSON.parse("{name: 'Ada'}");
} catch (err) {
  console.log("Invalid JSON:", err.name);
}

Learn JSON false
Invalid JSON: SyntaxError

Invalid JSON throws a SyntaxError, so wrap JSON.parse in try...catch when the input comes from outside your code.