The JavaScript JSON.stringify() method

Q: How do I pretty-print JSON in JavaScript?

Pass an indentation as the third argument: JSON.stringify(obj, null, 2) indents with two spaces.

Q: Why are some properties missing from the JSON?

Values of undefined, functions and symbols are dropped from objects. Dates are converted to ISO strings.

Q: How do I deep-copy an object with JSON?

Use JSON.parse(JSON.stringify(obj)) for plain data — but note it loses functions, dates and undefined. structuredClone() handles those cases properly.

Method JavaScript All modern browsers Updated June 23, 2026

Quick answer

The JSON.stringify() method converts a JavaScript value into a JSON string. JSON.stringify({a: 1}) gives '{"a":1}'. You use it to send data to a server or save it in localStorage. Pass a third argument to pretty-print: JSON.stringify(obj, null, 2). Its inverse is JSON.parse().

Overview

JSON.stringify() turns a JavaScript object, array or value into a JSON-formatted string. This is how data leaves your program: you stringify it to send in a fetch() request body, to store in localStorage (which only holds strings), or to log a clean snapshot of an object.

The third argument controls formatting. JSON.stringify(obj, null, 2) pretty-prints with two-space indentation, which makes logs and files human-readable. The second argument, a replacer, can filter or transform which properties get included — pass an array of key names to keep only those.

A few things quietly get dropped or changed, and it's worth knowing them: undefined, functions and symbols are omitted from objects (and become null in arrays), and Date objects turn into ISO strings. It also throws on circular references. Round-tripping through JSON.stringify() then JSON.parse() is a common (shallow-safe) way to deep-copy plain data.

Syntax

const json = JSON.stringify(value)
const json = JSON.stringify(value, replacer, space)

JSON.stringify({ a: 1 })          // '{"a":1}'
JSON.stringify(obj, null, 2)      // pretty-printed

Parameters

The JSON.stringify() method accepts the following parameters.

Parameter	Description
`value`	The JavaScript value (object, array, etc.) to convert to a JSON string.
`replacer`	Optional. A function to transform values, or an array of key names to keep. Use `null` to include everything.
`space`	Optional. Indentation for pretty-printing — a number of spaces (e.g. `2`) or a string.

Example

Live example

<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const user = { name: 'Ada', roles: ['admin', 'editor'] };

  const compact = JSON.stringify(user);
  const pretty  = JSON.stringify(user, null, 2);

  document.getElementById('out').textContent =
    compact + '\n\n' + pretty;
</script>

Best practices

Pretty-print for humans with JSON.stringify(obj, null, 2).
Always pair it with JSON.parse() when round-tripping data.
Remember undefined, functions and symbols are dropped, and dates become strings.
Wrap it in try/catch for data that might contain circular references, which throw.

Frequently asked questions

What does JSON.stringify() do?

It converts a JavaScript value into a JSON string, for sending to a server or storing as text.

How do I pretty-print JSON in JavaScript?

Pass an indentation as the third argument: JSON.stringify(obj, null, 2) indents with two spaces.

Why are some properties missing from the JSON?

Values of undefined, functions and symbols are dropped from objects. Dates are converted to ISO strings.

How do I deep-copy an object with JSON?

Use JSON.parse(JSON.stringify(obj)) for plain data — but note it loses functions, dates and undefined. structuredClone() handles those cases properly.

JSON.parse() Math.abs()

References