structuredClone()

The global structuredClone() method creates a deep clone of a given value using the structured clone algorithm.

The method also allows transferable objects in the original value to be transferred rather than cloned to the new object. Transferred objects are detached from the original object and attached to the new object; they are no longer accessible in the original object.

Syntax

structuredClone(value)
structuredClone(value, transferables)

Parameters

value

The object to be cloned. This can be any structured-clonable type.

transferables Optional

An array of transferable objects in value that will be moved rather than cloned to the returned object.

Return value

The returned value is a deep copy of the original value.

Exceptions

DataCloneError DOMException

Thrown if any part of the input value is not serializable.

Description

This function can be used to deep copy JavaScript values. It also supports circular references, as shown below:

// Create an object with a value and a circular reference to itself.
const original = { name: "MDN" };
original.itself = original;

// Clone it
const clone = structuredClone(original);

console.assert(clone !== original); // the objects are not the same (not same identity)
console.assert(clone.name === "MDN"); // they do have the same values
console.assert(clone.itself === clone); // and the circular reference is preserved

Transferring values

Transferable objects (only) can be transferred rather than duplicated in the cloned object, using the optional parameter's transfer value. Transferring makes the original object unusable.

Note: A scenario where this might be useful is when asynchronously validating some data in a buffer before saving it. To avoid the buffer being modified before the data is saved, you can clone the buffer and validate that data. If you also transfer the data, any attempts to modify the original buffer will fail, preventing its accidental misuse.

The following code shows how to clone an array and transfer its underlying resources to the new object. On return, the original uInt8Array.buffer will be cleared.

// 16MB = 1024 * 1024 * 16
const uInt8Array = Uint8Array.from({ length: 1024 * 1024 * 16 }, (v, i) => i);

const transferred = structuredClone(uInt8Array, { transfer: [uInt8Array.buffer] });
console.log(uInt8Array.byteLength);  // 0

You can clone any number of objects and transfer any subset of those objects. For example, the code below would transfer arrayBuffer1 from the passed in value, but not arrayBuffer2.

const transferred = structuredClone(
   { x: { y: { z: arrayBuffer1, w: arrayBuffer2 } } },
   { transfer: [arrayBuffer1] });

Specifications

Specification
HTML Standard
# dom-structuredclone

Browser compatibility

BCD tables only load in the browser

See also