JSON.parse() Explained

What does JSON.parse() do?

JSON.parse() takes a JSON string and converts it into a real JavaScript value — an object, array, number, string, boolean, or null. It is the opposite of JSON.stringify(), which turns a JavaScript value back into a JSON string.

You reach for it whenever data arrives as text — a response from an API, a value read from localStorage, or the contents of a .json file — because you cannot access properties on a string. Parsing turns that text into a structure you can actually work with.

Syntax

JSON.parse(text)
JSON.parse(text, reviver)

• text — the JSON string to parse.
• reviver (optional) — a function that transforms each value as it is parsed.

Basic example

Pass a JSON string and get back an object you can read from:

const text = '{"name":"Ada","age":36,"admin":true}';
const user = JSON.parse(text);

console.log(user.name);  // "Ada"
console.log(user.age);   // 36
typeof user;             // "object"

Arrays and nested structures work the same way:

const data = JSON.parse('[1, 2, {"ok": true}]');
data[2].ok;  // true

The reviver function

The optional second argument lets you transform values during parsing. A common use is converting date strings back into Date objects:

const text = '{"event":"launch","date":"2026-06-28T10:00:00Z"}';

const obj = JSON.parse(text, (key, value) => {
  if (key === 'date') return new Date(value);
  return value;
});

obj.date instanceof Date;  // true

JSON.parse() vs JSON.stringify()

They are mirror images of each other — one decodes, the other encodes:

Handling errors

If the string is not valid JSON, JSON.parse() throws a SyntaxError. Always wrap it in a try...catch when the input might be malformed:

function safeParse(text) {
  try {
    return JSON.parse(text);
  } catch (err) {
    console.error('Invalid JSON:', err.message);
    return null;
  }
}

The most frequent message is Unexpected token ... in JSON, usually caused by trailing commas, single quotes, unquoted keys, or an empty string. Our common JSON errors guide covers each one and how to fix it.

Decoding JSON in other languages

Every major language has an equivalent of JSON.parse() for decoding a JSON string:

import json
data = json.loads('{"name": "Ada"}')
data["name"]  # "Ada"

$data = json_decode('{"name": "Ada"}', true);
echo $data["name"]; // Ada

Frequently asked questions