JSON.parse and JSON.stringify in JavaScript: Complete Guide

The two core functions#

JavaScript has two built-in functions for JSON:

• JSON.parse(text) converts a JSON string into a JavaScript value.
• JSON.stringify(value) converts a JavaScript value into a JSON string.

const text = '{"name":"Ada","age":36}';
const user = JSON.parse(text);
console.log(user.age); // 36
 
const out = JSON.stringify(user);
console.log(out); // {"name":"Ada","age":36}

Always handle parse errors#

JSON.parse throws a SyntaxError on invalid input, so wrap untrusted input in try/catch.

function safeParse(text) {
  try {
    return { ok: true, value: JSON.parse(text) };
  } catch (error) {
    return { ok: false, error: error.message };
  }
}

If you do not know why a string fails, paste it into the NiceJSON validator to locate the error.

Pretty printing with stringify#

The third argument sets indentation:

JSON.stringify({ a: 1, b: [1, 2] }, null, 2);

The second argument is the replacer. Pass an array to pick keys, or a function to transform values:

const user = { name: "Ada", password: "secret", age: 36 };
 
JSON.stringify(user, ["name", "age"]);
// {"name":"Ada","age":36}
 
JSON.stringify(user, (key, value) =>
  key === "password" ? undefined : value
);

Reviving values with parse#

JSON.parse takes an optional reviver that runs on each value. It is the standard way to turn date strings back into Date objects.

const text = '{"created":"2026-11-04T10:00:00.000Z"}';
 
const obj = JSON.parse(text, (key, value) =>
  key === "created" ? new Date(value) : value
);
 
console.log(obj.created instanceof Date); // true

What stringify drops or changes#

Fixing BigInt#

JSON.stringify({ id: 12345678901234567890n }, (_, v) =>
  typeof v === "bigint" ? v.toString() : v
);

Circular references#

const a = {};
a.self = a;
JSON.stringify(a); // TypeError: Converting circular structure to JSON

Break the cycle manually, or use a library that supports reference handling.

Deep copy caveat#

JSON.parse(JSON.stringify(x)) is a common deep clone trick, but it loses dates, undefined, Map, and Set. Prefer structuredClone(x) in modern runtimes.

Security reminder#

Never use eval() to parse JSON. JSON.parse is safe because it only accepts data, never executable code.