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.
转载于:https://stackoverflow.com/questions/122102/what-is-the-most-efficient-way-to-deep-clone-an-object-in-javascript
Note: This is a reply to another answer, not a proper response to this question. If you wish to have fast object cloning please follow Corban's advice in their answer to this question.
I want to note that the .clone() method in jQuery only clones DOM elements. In order to clone JavaScript objects, you would do:
// Shallow copy
var newObject = jQuery.extend({}, oldObject);
// Deep copy
var newObject = jQuery.extend(true, {}, oldObject);
More information can be found in the jQuery documentation.
I also want to note that the deep copy is actually much smarter than what is shown above – it's able to avoid many traps (trying to deep extend a DOM element, for example). It's used frequently in jQuery core and in plugins to great effect.
Code:
// extends 'from' object with members from 'to'. If 'to' is null, a deep clone of 'from' is returned
function extend(from, to)
{
if (from == null || typeof from != "object") return from;
if (from.constructor != Object && from.constructor != Array) return from;
if (from.constructor == Date || from.constructor == RegExp || from.constructor == Function ||
from.constructor == String || from.constructor == Number || from.constructor == Boolean)
return new from.constructor(from);
to = to || new from.constructor();
for (var name in from)
{
to[name] = typeof to[name] == "undefined" ? extend(from[name], null) : to[name];
}
return to;
}
Test:
var obj =
{
date: new Date(),
func: function(q) { return 1 + q; },
num: 123,
text: "asdasd",
array: [1, "asd"],
regex: new RegExp(/aaa/i),
subobj:
{
num: 234,
text: "asdsaD"
}
}
var clone = extend(obj);
Shallow copy one-liner (ECMAScript 5th edition):
var origin = { foo : {} };
var copy = Object.keys(origin).reduce(function(c,k){c[k]=origin[k];return c;},{});
console.log(origin, copy);
console.log(origin == copy); // false
console.log(origin.foo == copy.foo); // true
And shallow copy one-liner (ECMAScript 6th edition, 2015):
var origin = { foo : {} };
var copy = Object.assign({}, origin);
console.log(origin, copy);
console.log(origin == copy); // false
console.log(origin.foo == copy.foo); // true
There seems to be no ideal deep clone operator yet for array-like objects. As the code below illustrates, John Resig's jQuery cloner turns arrays with non-numeric properties into objects that are not arrays, and RegDwight's JSON cloner drops the non-numeric properties. The following tests illustrate these points on multiple browsers:
function jQueryClone(obj) {
return jQuery.extend(true, {}, obj)
}
function JSONClone(obj) {
return JSON.parse(JSON.stringify(obj))
}
var arrayLikeObj = [[1, "a", "b"], [2, "b", "a"]];
arrayLikeObj.names = ["m", "n", "o"];
var JSONCopy = JSONClone(arrayLikeObj);
var jQueryCopy = jQueryClone(arrayLikeObj);
alert("Is arrayLikeObj an array instance?" + (arrayLikeObj instanceof Array) +
"\nIs the jQueryClone an array instance? " + (jQueryCopy instanceof Array) +
"\nWhat are the arrayLikeObj names? " + arrayLikeObj.names +
"\nAnd what are the JSONClone names? " + JSONCopy.names)
This isn't generally the most efficient solution, but it does what I need. Simple test cases below...
function clone(obj, clones) {
// Makes a deep copy of 'obj'. Handles cyclic structures by
// tracking cloned obj's in the 'clones' parameter. Functions
// are included, but not cloned. Functions members are cloned.
var new_obj,
already_cloned,
t = typeof obj,
i = 0,
l,
pair;
clones = clones || [];
if (obj === null) {
return obj;
}
if (t === "object" || t === "function") {
// check to see if we've already cloned obj
for (i = 0, l = clones.length; i < l; i++) {
pair = clones[i];
if (pair[0] === obj) {
already_cloned = pair[1];
break;
}
}
if (already_cloned) {
return already_cloned;
} else {
if (t === "object") { // create new object
new_obj = new obj.constructor();
} else { // Just use functions as is
new_obj = obj;
}
clones.push([obj, new_obj]); // keep track of objects we've cloned
for (key in obj) { // clone object members
if (obj.hasOwnProperty(key)) {
new_obj[key] = clone(obj[key], clones);
}
}
}
}
return new_obj || obj;
}
Cyclic array test...
a = []
a.push("b", "c", a)
aa = clone(a)
aa === a //=> false
aa[2] === a //=> false
aa[2] === a[2] //=> false
aa[2] === aa //=> true
Function test...
f = new Function
f.a = a
ff = clone(f)
ff === f //=> true
ff.a === a //=> false
function clone(obj)
{ var clone = {};
clone.prototype = obj.prototype;
for (property in obj) clone[property] = obj[property];
return clone;
}
I know this is an old post, but I thought this may be of some help to the next person who stumbles along.
As long as you don't assign an object to anything it maintains no reference in memory. So to make an object that you want to share among other objects, you'll have to create a factory like so:
var a = function(){
return {
father:'zacharias'
};
},
b = a(),
c = a();
c.father = 'johndoe';
alert(b.father);
There’s a library (called “clone”), that does this quite well. It provides the most complete recursive cloning/copying of arbitrary objects that I know of. It also supports circular references, which is not covered by the other answers, yet.
You can find it on npm, too. It can be used for the browser as well as Node.js.
Here is an example on how to use it:
Install it with
npm install clone
or package it with Ender.
ender build clone [...]
You can also download the source code manually.
Then you can use it in your source code.
var clone = require('clone');
var a = { foo: { bar: 'baz' } }; // inital value of a
var b = clone(a); // clone a -> b
a.foo.bar = 'foo'; // change a
console.log(a); // { foo: { bar: 'foo' } }
console.log(b); // { foo: { bar: 'baz' } }
(Disclaimer: I’m the author of the library.)
var clone = function() {
var newObj = (this instanceof Array) ? [] : {};
for (var i in this) {
if (this[i] && typeof this[i] == "object") {
newObj[i] = this[i].clone();
}
else
{
newObj[i] = this[i];
}
}
return newObj;
};
Object.defineProperty( Object.prototype, "clone", {value: clone, enumerable: false});
Here's a version of ConroyP's answer above that works even if the constructor has required parameters:
//If Object.create isn't already defined, we just do the simple shim,
//without the second argument, since that's all we need here
var object_create = Object.create;
if (typeof object_create !== 'function') {
object_create = function(o) {
function F() {}
F.prototype = o;
return new F();
};
}
function deepCopy(obj) {
if(obj == null || typeof(obj) !== 'object'){
return obj;
}
//make sure the returned object has the same prototype as the original
var ret = object_create(obj.constructor.prototype);
for(var key in obj){
ret[key] = deepCopy(obj[key]);
}
return ret;
}
This function is also available in my simpleoo library.
Edit:
Here's a more robust version (thanks to Justin McCandless this now supports cyclic references as well):
/**
* Deep copy an object (make copies of all its object properties, sub-properties, etc.)
* An improved version of http://keithdevens.com/weblog/archive/2007/Jun/07/javascript.clone
* that doesn't break if the constructor has required parameters
*
* It also borrows some code from http://stackoverflow.com/a/11621004/560114
*/
function deepCopy(src, /* INTERNAL */ _visited, _copiesVisited) {
if(src === null || typeof(src) !== 'object'){
return src;
}
//Honor native/custom clone methods
if(typeof src.clone == 'function'){
return src.clone(true);
}
//Special cases:
//Date
if(src instanceof Date){
return new Date(src.getTime());
}
//RegExp
if(src instanceof RegExp){
return new RegExp(src);
}
//DOM Element
if(src.nodeType && typeof src.cloneNode == 'function'){
return src.cloneNode(true);
}
// Initialize the visited objects arrays if needed.
// This is used to detect cyclic references.
if (_visited === undefined){
_visited = [];
_copiesVisited = [];
}
// Check if this object has already been visited
var i, len = _visited.length;
for (i = 0; i < len; i++) {
// If so, get the copy we already made
if (src === _visited[i]) {
return _copiesVisited[i];
}
}
//Array
if (Object.prototype.toString.call(src) == '[object Array]') {
//[].slice() by itself would soft clone
var ret = src.slice();
//add it to the visited array
_visited.push(src);
_copiesVisited.push(ret);
var i = ret.length;
while (i--) {
ret[i] = deepCopy(ret[i], _visited, _copiesVisited);
}
return ret;
}
//If we've reached here, we have a regular object
//make sure the returned object has the same prototype as the original
var proto = (Object.getPrototypeOf ? Object.getPrototypeOf(src): src.__proto__);
if (!proto) {
proto = src.constructor.prototype; //this line would probably only be reached by very old browsers
}
var dest = object_create(proto);
//add this object to the visited array
_visited.push(src);
_copiesVisited.push(dest);
for (var key in src) {
//Note: this does NOT preserve ES5 property attributes like 'writable', 'enumerable', etc.
//For an example of how this could be modified to do so, see the singleMixin() function
dest[key] = deepCopy(src[key], _visited, _copiesVisited);
}
return dest;
}
//If Object.create isn't already defined, we just do the simple shim,
//without the second argument, since that's all we need here
var object_create = Object.create;
if (typeof object_create !== 'function') {
object_create = function(o) {
function F() {}
F.prototype = o;
return new F();
};
}
Here is a comprehensive clone() method that can clone any JavaScript object. It handles almost all the cases:
function clone(src, deep) {
var toString = Object.prototype.toString;
if (!src && typeof src != "object") {
// Any non-object (Boolean, String, Number), null, undefined, NaN
return src;
}
// Honor native/custom clone methods
if (src.clone && toString.call(src.clone) == "[object Function]") {
return src.clone(deep);
}
// DOM elements
if (src.nodeType && toString.call(src.cloneNode) == "[object Function]") {
return src.cloneNode(deep);
}
// Date
if (toString.call(src) == "[object Date]") {
return new Date(src.getTime());
}
// RegExp
if (toString.call(src) == "[object RegExp]") {
return new RegExp(src);
}
// Function
if (toString.call(src) == "[object Function]") {
//Wrap in another method to make sure == is not true;
//Note: Huge performance issue due to closures, comment this :)
return (function(){
src.apply(this, arguments);
});
}
var ret, index;
//Array
if (toString.call(src) == "[object Array]") {
//[].slice(0) would soft clone
ret = src.slice();
if (deep) {
index = ret.length;
while (index--) {
ret[index] = clone(ret[index], true);
}
}
}
//Object
else {
ret = src.constructor ? new src.constructor() : {};
for (var prop in src) {
ret[prop] = deep
? clone(src[prop], true)
: src[prop];
}
}
return ret;
};
This is what I'm using:
function cloneObject(obj) {
var clone = {};
for(var i in obj) {
if(typeof(obj[i])=="object" && obj[i] != null)
clone[i] = cloneObject(obj[i]);
else
clone[i] = obj[i];
}
return clone;
}
Crockford suggests (and I prefer) using this function:
function object(o) {
function F() {}
F.prototype = o;
return new F();
}
var newObject = object(oldObject);
It's terse, works as expected and you don't need a library.
EDIT:
This is a polyfill for Object.create, so you also can use this.
var newObject = Object.create(oldObject);
NOTE: If you use some of this, you may have problems with some iteration who use hasOwnProperty. Because, create create new empty object who inherits oldObject. But it is still useful and practical for cloning objects.
For exemple if oldObject.a = 5;
newObject.a; // is 5
but:
oldObject.hasOwnProperty(a); // is true
newObject.hasOwnProperty(a); // is false
If you're using it, the Underscore.js library has a clone method.
var newObject = _.clone(oldObject);
// obj target object, vals source object
var setVals = function (obj, vals) {
if (obj && vals) {
for (var x in vals) {
if (vals.hasOwnProperty(x)) {
if (obj[x] && typeof vals[x] === 'object') {
obj[x] = setVals(obj[x], vals[x]);
} else {
obj[x] = vals[x];
}
}
}
}
return obj;
};
If there wasn't any builtin one, 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);
else
var temp = obj.constructor();
for (var key in obj) {
if (Object.prototype.hasOwnProperty.call(obj, key)) {
obj['isActiveClone'] = null;
temp[key] = clone(obj[key]);
delete obj['isActiveClone'];
}
}
return temp;
}
Assuming that you have only variables and not any functions in your object, you can just use:
var newObject = JSON.parse(JSON.stringify(oldObject));
Checkout this benchmark: http://jsben.ch/#/bWfk9
In my previous tests where speed was a main concern I found
JSON.parse(JSON.stringify(obj))
to be the fastest way to deep clone an object (it beats out jQuery.extend with deep flag set true by 10-20%).
jQuery.extend is pretty fast when the deep flag is set to false (shallow clone). It is a good option, because it includes some extra logic for type validation and doesn't copy over undefined properties, etc., but this will also slow you down a little.
If you know the structure of the objects you are trying to clone or can avoid deep nested arrays you can write a simple for (var i in obj) loop to clone your object while checking hasOwnProperty and it will be much much faster than jQuery.
Lastly if you are attempting to clone a known object structure in a hot loop you can get MUCH MUCH MORE PERFORMANCE by simply in-lining the clone procedure and manually constructing the object.
JavaScript trace engines suck at optimizing for..in loops and checking hasOwnProperty will slow you down as well. Manual clone when speed is an absolute must.
var clonedObject = {
knownProp: obj.knownProp,
..
}
Beware using the JSON.parse(JSON.stringify(obj)) method on Date objects - JSON.stringify(new Date()) returns a string representation of the date in ISO format, which JSON.parse() doesn't convert back to a Date object. See this answer for more details.
Additionally, please note that, in Chrome 65 at least, native cloning is not the way to go. According to this JSPerf, performing native cloning by creating a new function is nearly 800x slower than using JSON.stringify which is incredibly fast all the way across the board.
I have two good answers depending on whether your objective is to clone a "plain old JavaScript object" or not.
Let's also assume that your intention is to create a complete clone with no prototype references back to the source object. If you're not interested in a complete clone, then you can use many of the Object.clone() routines provided in some of the other answers (Crockford's pattern).
For plain old JavaScript objects, a tried and true good way to clone an object in modern runtimes is quite simply:
var clone = JSON.parse(JSON.stringify(obj));
Note that the source object must be a pure JSON object. This is to say, all of its nested properties must be scalars (like boolean, string, array, object, etc). Any functions or special objects like RegExp or Date will not be cloned.
Is it efficient? Heck yes. We've tried all kinds of cloning methods and this works best. I'm sure some ninja could conjure up a faster method. But I suspect we're talking about marginal gains.
This approach is just simple and easy to implement. Wrap it into a convenience function and if you really need to squeeze out some gain, go for at a later time.
Now, for non-plain JavaScript objects, there isn't a really simple answer. In fact, there can't be because of the dynamic nature of JavaScript functions and inner object state. Deep cloning a JSON structure with functions inside requires you recreate those functions and their inner context. And JavaScript simply doesn't have a standardized way of doing that.
The correct way to do this, once again, is via a convenience method that you declare and reuse within your code. The convenience method can be endowed with some understanding of your own objects so you can make sure to properly recreate the graph within the new object.
We're written our own, but the best general approach I've seen is covered here:
http://davidwalsh.name/javascript-clone
This is the right idea. The author (David Walsh) has commented out the cloning of generalized functions. This is something you might choose to do, depending on your use case.
The main idea is that you need to special handle the instantiation of your functions (or prototypal classes, so to speak) on a per-type basis. Here, he's provided a few examples for RegExp and Date.
Not only is this code brief, but it's also very readable. It's pretty easy to extend.
Is this efficient? Heck yes. Given that the goal is to produce a true deep-copy clone, then you're going to have to walk the members of the source object graph. With this approach, you can tweak exactly which child members to treat and how to manually handle custom types.
So there you go. Two approaches. Both are efficient in my view.
Lodash has a nice _.cloneDeep(value) method:
var objects = [{ 'a': 1 }, { 'b': 2 }];
var deep = _.cloneDeep(objects);
console.log(deep[0] === objects[0]);
// => false
I usually use var newObj = JSON.parse( JSON.stringify(oldObje) ); but, here's a more proper way:
var o = {};
var oo = Object.create(o);
(o === oo); // => false
Watch legacy browsers!
Deep copy by performance: Ranked from best to worst
Deep copy an array of strings or numbers (one level - no reference pointers):
When an array contains numbers and strings - functions like .slice(), .concat(), .splice(), the assignment operator "=", and Underscore.js's clone function; will make a deep copy of the array's elements.
Where reassignment has the fastest performance:
var arr1 = ['a', 'b', 'c'];
var arr2 = arr1;
arr1 = ['a', 'b', 'c'];
And .slice() has better performance than .concat(), http://jsperf.com/duplicate-array-slice-vs-concat/3
var arr1 = ['a', 'b', 'c']; // Becomes arr1 = ['a', 'b', 'c']
var arr2a = arr1.slice(0); // Becomes arr2a = ['a', 'b', 'c'] - deep copy
var arr2b = arr1.concat(); // Becomes arr2b = ['a', 'b', 'c'] - deep copy
Deep copy an array of objects (two or more levels - reference pointers):
var arr1 = [{object:'a'}, {object:'b'}];
Write a custom function (has faster performance than $.extend() or JSON.parse):
function copy(o) {
var out, v, key;
out = Array.isArray(o) ? [] : {};
for (key in o) {
v = o[key];
out[key] = (typeof v === "object" && v !== null) ? copy(v) : v;
}
return out;
}
copy(arr1);
Use third-party utility functions:
$.extend(true, [], arr1); // Jquery Extend
JSON.parse(arr1);
_.cloneDeep(arr1); // Lo-dash
Where jQuery's $.extend has better performance:
The following creates two instances of the same object. I found it and am using it currently. It's simple and easy to use.
var objToCreate = JSON.parse(JSON.stringify(cloneThis));
For the people who want to use the JSON.parse(JSON.stringify(obj)) version, but without losing the Date objects, you can use the second argument of parse method to convert the strings back to Date:
function clone(obj) {
var regExp = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/;
return JSON.parse(JSON.stringify(x), function(k, v) {
if (typeof v === 'string' && regExp.test(v))
return new Date(v);
return v;
});
}
An Object.assign method is part of the ECMAScript 2015 (ES6) standard and does exactly what you need.
var clone = Object.assign({}, obj);
The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object.
The polyfill to support older browsers:
if (!Object.assign) {
Object.defineProperty(Object, 'assign', {
enumerable: false,
configurable: true,
writable: true,
value: function(target) {
'use strict';
if (target === undefined || target === null) {
throw new TypeError('Cannot convert first argument to object');
}
var to = Object(target);
for (var i = 1; i < arguments.length; i++) {
var nextSource = arguments[i];
if (nextSource === undefined || nextSource === null) {
continue;
}
nextSource = Object(nextSource);
var keysArray = Object.keys(nextSource);
for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
var nextKey = keysArray[nextIndex];
var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
if (desc !== undefined && desc.enumerable) {
to[nextKey] = nextSource[nextKey];
}
}
}
return to;
}
});
}
Just because I didn't see AngularJS mentioned and thought that people might want to know...
angular.copy also provides a method of deep copying objects and arrays.
Well if you're using angular you could do this too
var newObject = angular.copy(oldObject);
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:
1) 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();
copy.setTime(obj.getTime());
return copy;
}
if (obj instanceof Array) {
var copy = [];
for (var i = 0, len = obj.length; i < len; i++) {
copy[i] = cloneSO(obj[i]);
}
return copy;
}
if (obj instanceof Object) {
var copy = {};
for (var attr in obj) {
if (obj.hasOwnProperty(attr)) copy[attr] = cloneSO(obj[attr]);
}
return copy;
}
throw new Error("Unable to copy obj this object.");
}
2) ES5+, using JSON.parse and JSON.stringify.
var deepCopyObj = JSON.parse(JSON.stringify(obj));
3) AngularJs:
var deepCopyObj = angular.copy(obj);
4) jQuery:
var deepCopyObj = jQuery.extend(true, {}, obj);
5) UnderscoreJs & Loadash:
var deepCopyObj = _.cloneDeep(obj); //latest version UndescoreJs makes shallow copy
Hope these help...
I disagree with the answer with the greatest votes here. A Recursive Deep Clone is much faster than the JSON.parse(JSON.stringify(obj)) approach mentioned.
And here's the function for quick reference:
function cloneDeep (o) {
let newO
let i
if (typeof o !== 'object') return o
if (!o) return o
if (Object.prototype.toString.apply(o) === '[object Array]') {
newO = []
for (i = 0; i < o.length; i += 1) {
newO[i] = cloneDeep(o[i])
}
return newO
}
newO = {}
for (i in o) {
if (o.hasOwnProperty(i)) {
newO[i] = cloneDeep(o[i])
}
}
return newO
}