What does structuredClone() do?

JavaScriptJunior~1 min read

What structuredClone() does

structuredClone() is a built-in JavaScript function that creates a deep clone of any value, including objects, arrays, maps, sets, dates, RegExp, Blob, File, ArrayBuffer and even circular references.

Syntax:

javascript

const clone = structuredClone(value);

value is what needs to be cloned;
it returns a new, independent object, fully copied.

Example of basic usage

javascript

const user = {
  name: "Tim",
  age: 25,
  skills: ["JS", "React"],
  meta: { active: true },
};

const copy = structuredClone(user);

copy.meta.active = false;
console.log(user.meta.active); // true - the original did not change

Here structuredClone() created a new copy, not a reference to the same object (unlike shallow copying with {...user}).

The main difference from JSON.parse(JSON.stringify(...))

Deep copying used to often rely on:

javascript

const copy = JSON.parse(JSON.stringify(obj));

But this approach has many limitations:

Data type	JSON method	structuredClone
`Date`	turns into a string	preserved as `Date`
`Map`, `Set`	lost	copied
`undefined`	disappears	preserved
`RegExp`, `Error`	lost	preserved
`NaN`, `Infinity`	turn into `null`	preserved
Circular references	error	supported

So structuredClone() is a reliable, safe deep-clone alternative that supports every type.

Example with circular references

javascript

const obj = {};
obj.self = obj; // circular reference

const clone = structuredClone(obj);
console.log(clone.self === clone); // true

This kind of cloning used to simply throw a TypeError.

Cloning with transferring binary data (optional)

structuredClone has a second argument - options that let you transfer (instead of copy) certain objects (for example, ArrayBuffer).

javascript

const buffer = new ArrayBuffer(8);
const clone = structuredClone(buffer, { transfer: [buffer] });

console.log(buffer.byteLength); // 0 - the original was "transferred" (detached)
console.log(clone.byteLength);  // 8 - the data is now on the clone

This works similarly to Transferable objects in postMessage.

Where it works

Supported in all modern browsers and in Node.js (starting from v17+):

javascript

structuredClone({ test: true }); // works in Node 17+

Summary

Point	Description
What it does	Deeply clones a value of any type
Returns	A full, independent copy
Supports	`Date`, `Map`, `Set`, `RegExp`, `ArrayBuffer`, circular references
Does not support	Functions, DOM elements
Compatibility	Modern browsers and Node.js 17+
Alternative to	A safe replacement for `JSON.parse(JSON.stringify())`

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