JSON in JavaScript — Parse, Stringify & Fetch

JavaScript has native JSON support through the global JSON object. JSON was designed with JavaScript in mind, so the integration is seamless.

Parse a JSON string

Use JSON.parse() to convert a JSON string into a JavaScript object or array.

const jsonString = '{"name":"Alice","age":30,"active":true}';
const data = JSON.parse(jsonString);

console.log(data.name);   // Alice
console.log(data.age);    // 30
console.log(typeof data); // object

Serialize to JSON

Use JSON.stringify() to convert a JavaScript value to a JSON string. Pass null, 2 as the second and third arguments for pretty-printing.

const data = { name: "Alice", scores: [95, 87], active: true };

// Compact
const compact = JSON.stringify(data);
// {"name":"Alice","scores":[95,87],"active":true}

// Pretty-printed
const pretty = JSON.stringify(data, null, 2);
console.log(pretty);

Fetch JSON from an API

The Fetch API returns a Response object. Call .json() to parse the body as JSON.

const response = await fetch("https://api.example.com/users/1");

if (!response.ok) {
  throw new Error(`HTTP error: ${response.status}`);
}

const user = await response.json();
console.log(user.name);

Handle parse errors

JSON.parse() throws a SyntaxError on invalid JSON. Always wrap in try/catch when handling untrusted input.

try {
  const data = JSON.parse('{"name": "Alice", invalid}');
} catch (err) {
  if (err instanceof SyntaxError) {
    console.error("Invalid JSON:", err.message);
  }
}

Deep clone with JSON

A common pattern to deep-clone a plain object (no functions, no undefined, no circular refs).

const original = { a: 1, b: { c: 2 } };
const clone = JSON.parse(JSON.stringify(original));

clone.b.c = 99;
console.log(original.b.c); // 2 — original unchanged

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