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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.

2 Answers

you could try:

function clone(obj) {
if (obj === null || typeof (obj) !== 'object' || 'isActiveClone' in obj)
return obj;

if (obj instanceof Date)
var temp = new obj.constructor(); //or new Date(obj);
var temp = obj.constructor();

for (var key in obj) {
if (, key)) {
obj['isActiveClone'] = null;
temp[key] = clone(obj[key]);
delete obj['isActiveClone'];
return temp;
Cloning an Object was always a concern in JS, but it was all about before ES6, I list different ways of copying an object in JavaScript below, imagine you have the Object below and would like to have a deep copy of that:

var obj = {a:1, b:2, c:3, d:4};

There are few ways to copy this object, without changing the origin:

ES5+, Using a simple function to do the copy for you:
function deepCopyObj(obj) {
if (null == obj || "object" != typeof obj) return obj;
if (obj instanceof Date) {
var copy = new Date();
return copy;
if (obj instanceof Array) {
var copy = [];
for (var i = 0, len = obj.length; i < len; i++) {
copy[i] = deepCopyObj(obj[i]);
return copy;
if (obj instanceof Object) {
var copy = {};
for (var attr in obj) {
if (obj.hasOwnProperty(attr)) copy[attr] = deepCopyObj(obj[attr]);
return copy;
throw new Error("Unable to copy obj this object.");

ES5+, using JSON.parse and JSON.stringify.

var deepCopyObj = JSON.parse(JSON.stringify(obj));


var deepCopyObj = angular.copy(obj);


var deepCopyObj = jQuery.extend(true, {}, obj);

UnderscoreJs & Loadash:

var deepCopyObj = _.cloneDeep(obj); //latest version UndescoreJs makes shallow copy

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