What is the most efficient way to deep clone an object in JavaScript?

What is the most efficient way to clone a JavaScript object? I've seen obj = eval(uneval(o)); being used, but that's non-standard and only supported by Firefox.

I've done things like obj = JSON.parse(JSON.stringify(o)); but question the efficiency.

I've also seen recursive copying functions with various flaws.

I'm surprised no canonical solution exists.

Native deep cloning

There's now a structuredClone(value) function supported in all major browsers and node >= 17. It has polyfills for older systems.

structuredClone(value)

If needed, loading the polyfill first:

import structuredClone from '@ungap/structured-clone';

See this answer for more details, but note these limitations:

• Function objects cannot be duplicated by the structured clone algorithm; attempting to throws a DataCloneError exception.

• Cloning DOM nodes likewise throws a DataCloneError exception.

• Certain object properties are not preserved:

• The lastIndex property of RegExp objects is not preserved.

• Property descriptors, setters, getters, and similar metadata-like features are not duplicated. For example, if an object is marked readonly with a property descriptor, it will be read/write in the duplicate, since that's the default.

• The prototype chain is not walked or duplicated.

Older answers
Fast cloning with data loss - JSON.parse/stringify

If you do not use Dates, functions, undefined, Infinity, RegExps, Maps, Sets, Blobs, FileLists, ImageDatas, sparse Arrays, Typed Arrays or other complex types within your object, a very simple one liner to deep clone an object is:

JSON.parse(JSON.stringify(object))



const a = {
string: 'string',
number: 123,
bool: false,
nul: null,
date: new Date(), // stringified
undef: undefined, // lost
inf: Infinity, // forced to 'null'
re: /.*/, // lost
}
console.log(a);
console.log(typeof a.date); // Date object
const clone = JSON.parse(JSON.stringify(a));
console.log(clone);
console.log(typeof clone.date); // result of .toISOString()



See Corban's answer for benchmarks.
Reliable cloning using a library

Since cloning objects is not trivial (complex types, circular references, function etc.), most major libraries provide function to clone objects. Don't reinvent the wheel - if you're already using a library, check if it has an object cloning function. For example,

• lodash - cloneDeep; can be imported separately via the lodash.clonedeep module and is probably your best choice if you're not already using a library that provides a deep cloning function

• Ramda - clone

• AngularJS - angular.copy

• jQuery - jQuery.extend(true, { }, oldObject); .clone() only clones DOM elements

• just library - just-clone; Part of a library of zero-dependency npm modules that do just do one thing.

Guilt-free utilities for every occasion.

Stack Overflow Q#122102, score: 6002