We Keep Coding

Replace Symbol Keys in Object With Text

I have the following object like this:
{ where: { [Symbol(or)]: [ [Object], [Object] ] },hooks: true, rejectOnEmpty: false }
I'm calling JSON.stringify on this, and it gets converted to:
{"where":{},"hooks":true,"rejectOnEmpty":false}
I think this is because [Symbol(or)] evaluates to undefined so stringify removes it.
This value is coming from Sequelize operators, specifically Op.or. Is there a way stringify can convert this to a String so I would instead receive:
{"where":{"[Symbol(or)]": [[<<stringifiedObject>>], [<<stringifiedObject>>]]},"hooks":true,"rejectOnEmpty":false}
I know I could pass a function to JSON.stringify which would replace undefined with something, but I would like to maintain the original Symbol in the string replacement, so that I can distinguish between Symbol(and) and Symbol(or), even though both would evaluate to undefined.

Solved with the following function:
const cleanObject = (obj) => {
try {
const keys = Reflect.ownKeys(obj);
const ret = {};
keys.forEach((key) => {
let val = obj[key];
if (Object.prototype.toString.call(val) === '[object Object]') {
val = cleanObject(val);
}
if (typeof key === 'symbol') {
const newKey = `${String(key)}`;
ret[newKey] = val;
} else {
ret[key] = val;
}
});
return ret;
} catch (ex) {
console.log(ex);
}
};
Reflect.ownKeys returns all keys, including Symbols.
Next, I check if a given key is a Symbol and replace it with a string. I also call the function recursively to apply the same logic to all nested objects.

How to delete empty instances from an array while using a recursive clean function?

To give some background: By using Postman (the REST api tool) we are comparing XMLs to a template by converting the XMLs to JSON and compare those as Javascript objects. The comparison can handle wildcards in the values and will return a new JS object (or JSON) with only the differences. When there are no differences, I receive an empty object which is the correct state. In some cases empty values or objects are returned and we remove them from the object with a clean step.
This is how the clean function looks like:
Utils = {
clean: function(object) {
Object
.entries(object)
.forEach(([k, v]) => {
if (v && typeof v === 'object')
Utils.clean(v);
if (v && typeof v === 'object' && !Object.keys(v).length || v === null || v === undefined)
Array.isArray(object) ? object.splice(k, 1) : delete object[k];
});
return object;
}
}
This works fine for most cases except when we have an array with multiple the same empty object because of the object.splice in combination with the foreach as pointed out here.
Normally, I would use a filter function, use _.pickBy from lodash or iterate backwards through the array, but because of the layout of the clean function, I can not figure out how to do that.
Can you help me to point out what I need to do to remove multiple empty items and objects from an array correctly.
Real life testcase:
var x = {"Document":{"CstmrDrctDbtInitn":{"GrpHdr":{},"PmtInf":{"DrctDbtTxInf":[{"PmtId":{}},{"PmtId":{}},{"PmtId":{}},{"PmtId":{}},{"PmtId":{}}]}}}};
console.log(JSON.stringify(Utils.clean(x)));
// returns {"Document":{"CstmrDrctDbtInitn":{"PmtInf":{"DrctDbtTxInf":[{},{}]}}}}
// desired result: {}
Other testcases:
console.log(JSON.stringify(Utils.clean({"a": [null,null,"b","c",{},{},{},{}]})));
// returns {"a":[null,"c",{},{},{}]}
// desired: {"a":["b", "c"]}
console.log(JSON.stringify(Utils.clean({"a": [null,null,"b","c",{"d": {}},{}]})));
// returns {"a":[null,"c",{},{}]}
// desired: {"a":["b", "c"]}
console.log(JSON.stringify(Utils.clean({ "a" : [null,null,{"d": {}, "e": [null, {}]},{}]})));
// returns {"a":[null,{}]}
// desired: {}

Give this a shot, and here's a working example: https://jsfiddle.net/3rno4L7d/
Utils Object (with extra helpers)
const Utils = {
doDelete: function(val) {
return !Boolean(val) ||
Utils.isEmptyObj(val) ||
Utils.isEmptyArray(val);
},
isEmptyArray: function(val) {
return Array.isArray(val) && val.length === 0;
},
isEmptyObj: function(obj) {
return Object.keys(obj).length === 0 &&
obj.constructor === Object;
},
hasKeys: function(obj) {
return Object.keys(obj).length > 0;
},
clean: function(object) {
Object
.keys(object)
.forEach(key => {
const val = object[key];
// If dealing with an object, clean it.
if (val && typeof val === 'object') {
Utils.clean(val);
}
// If deleteable, delete and return
if (Utils.doDelete(val)) {
delete object[key];
return object;
}
// If array, loop over entries
if (Array.isArray(val)) {
let i = val.length;
// While lets us delete from the array without affecting the loop.
while (i--) {
let entry = val[i];
// If deleteable, delete from the array
if (Utils.doDelete(entry)) {
val.splice(i, 1)
} else if (Utils.hasKeys(entry)) {
// If an object, clean it
entry = Utils.clean(entry);
// Check to see if cleaned object is deleteable
if (Utils.doDelete(entry)) {
val.splice(i, 1)
}
}
}
// Once done with the array, check if deleteable
if (Utils.doDelete(val)) {
delete object[key];
}
}
});
return object;
}
}
Output
console.log(JSON.stringify(Utils.clean({"a": [null,null,"b","c",{},{},{},{}]})));
// Returns {"a":["b","c"]}
console.log(JSON.stringify(Utils.clean({"a": [null,null,"b","c",{"d": {}},{}]})));
// Returns {"a":["b","c"]}
console.log(JSON.stringify(Utils.clean({ "a" : [null,null,{"d": {}, "e": [null, {}]},{}]})));
// Returns {}

How to check if every properties in an object are null

I have an object, sometimes it is empty like so {} other times it will have properties that are set to null.
{
property1: null,
property2: null
}
How can I determine if ALL the properties within this object is null?
If they are all null then return false.
At the moment I'm using lodash to check for the first case where the object is simply {} empty. But I also need to cover the second case.
if (isEmpty(this.report.device)) {
return false;
}
return true;

You can use Object.values to convert the object into array and use every to check each element. Use ! to negate the value.
let report = {
property1: null,
property2: null,
}
let result = !Object.values(report).every(o => o === null);
console.log(result);
An example some elements are not null
let report = {
property1: null,
property2: 1,
}
let result = !Object.values(report).every(o => o === null);
console.log(result);
Doc: Object.values(), every()

Approach using .some() instead of .every():
function isEmpty (obj) {
return !Object.values(obj).some(element => element !== null);
}
This function (named isEmpty to match the name given in the question) shall return false if any obj property is not null and true otherwise.

You can use the Object.keys() method this will return all keys in that Object as an Array. This makes it possible to do Object.keys(this.report.device).filter(key => !this.report.device[key] === null), which will return you the amount of not null keys, if this is 0 then you have your answer.
In essence relying on null properties is not such a good approach it's better to make those properties undefined or just to return a flat Object from your API.
Hope this helped.

This is very simple and can be done with a one liner !
function IsAllPropertiesNull(obj) {
return Object.values(obj).every(v=>v == null);
}
a = {'a': null, 'b':null};
var isAllNull = IsAllPropertiesNull(a)
// isAllNull = true
explanation -
get all values of object - iterate them and check for null
Good luck!

Use Object.entries and Array.every
let obj = {
property1: null,
property2: null,
};
function isEmpty(o) {
return Object.entries(o).every(([k,v]) => v === null);
}
if(isEmpty(obj)) {
console.log("Object is empty");
}

In order to check if object has null value for all the keys. One cleaner approach could be.
const set = new Set(Object.values(obj));
const hasOnlyNullValues = set.size === 1 && set.has(null);

For Es2015
if (Object.keys(obj).map(e => obj[e]).every(a => a.length === 0)) {
console.log('all are empty');
}

The most accurate way to check JS object's type?

The typeof operator doesn't really help us to find the real type of an object.
I've already seen the following code :
Object.prototype.toString.apply(t)
Question:
Is it the most accurate way of checking the object's type?

The JavaScript specification gives exactly one proper way to determine the class of an object:
Object.prototype.toString.call(t);
http://bonsaiden.github.io/JavaScript-Garden/#types

the Object.prototype.toString is a good way, but its performance is the worst.
http://jsperf.com/check-js-type
Use typeof to solve some basic problem(String, Number, Boolean...) and use Object.prototype.toString to solve something complex(like Array, Date, RegExp).
and this is my solution:
var type = (function(global) {
var cache = {};
return function(obj) {
var key;
return obj === null ? 'null' // null
: obj === global ? 'global' // window in browser or global in nodejs
: (key = typeof obj) !== 'object' ? key // basic: string, boolean, number, undefined, function
: obj.nodeType ? 'object' // DOM element
: cache[key = ({}).toString.call(obj)] // cached. date, regexp, error, object, array, math
|| (cache[key] = key.slice(8, -1).toLowerCase()); // get XXXX from [object XXXX], and cache it
};
}(this));
use as:
type(function(){}); // -> "function"
type([1, 2, 3]); // -> "array"
type(new Date()); // -> "date"
type({}); // -> "object"

Accepted answer is correct, but I like to define this little utility in most projects I build.
var types = {
'get': function(prop) {
return Object.prototype.toString.call(prop);
},
'null': '[object Null]',
'object': '[object Object]',
'array': '[object Array]',
'string': '[object String]',
'boolean': '[object Boolean]',
'number': '[object Number]',
'date': '[object Date]',
}
Used like this:
if(types.get(prop) == types.number) {
}
If you're using angular you can even have it cleanly injected:
angular.constant('types', types);

var o = ...
var proto = Object.getPrototypeOf(o);
proto === SomeThing;
Keep a handle on the prototype you expect the object to have, then compare against it.
for example
var o = "someString";
var proto = Object.getPrototypeOf(o);
proto === String.prototype; // true

I'd argue that most of the solutions shown here suffer from being over-engineerd. Probably the most simple way to check if a value is of type [object Object] is to check against the .constructor property of it:
function isObject (a) { return a != null && a.constructor === Object; }
or even shorter with arrow-functions:
const isObject = a => a != null && a.constructor === Object;
The a != null part is necessary because one might pass in null or undefined and you cannot extract a constructor property from either of these.
It works with any object created via:
the Object constructor
literals {}
Another neat feature of it, is it's ability to give correct reports for custom classes which make use of Symbol.toStringTag. For example:
class MimicObject {
get [Symbol.toStringTag]() {
return 'Object';
}
}
The problem here is that when calling Object.prototype.toString on an instance of it, the false report [object Object] will be returned:
let fakeObj = new MimicObject();
Object.prototype.toString.call(fakeObj); // -> [object Object]
But checking against the constructor gives a correct result:
let fakeObj = new MimicObject();
fakeObj.constructor === Object; // -> false

The best way to find out the REAL type of an object (including BOTH the native Object or DataType name (such as String, Date, Number, ..etc) AND the REAL type of an object (even custom ones); is by grabbing the name property of the object prototype's constructor:
Native Type Ex1:
var string1 = "Test";
console.log(string1.__proto__.constructor.name);
displays:
String
Ex2:
var array1 = [];
console.log(array1.__proto__.constructor.name);
displays:
Array
Custom Classes:
function CustomClass(){
console.log("Custom Class Object Created!");
}
var custom1 = new CustomClass();
console.log(custom1.__proto__.constructor.name);
displays:
CustomClass

Old question I know. You don't need to convert it. See this function:
function getType( oObj )
{
if( typeof oObj === "object" )
{
return ( oObj === null )?'Null':
// Check if it is an alien object, for example created as {world:'hello'}
( typeof oObj.constructor !== "function" )?'Object':
// else return object name (string)
oObj.constructor.name;
}
// Test simple types (not constructed types)
return ( typeof oObj === "boolean")?'Boolean':
( typeof oObj === "number")?'Number':
( typeof oObj === "string")?'String':
( typeof oObj === "function")?'Function':false;
};
Examples:
function MyObject() {}; // Just for example
console.log( getType( new String( "hello ") )); // String
console.log( getType( new Function() ); // Function
console.log( getType( {} )); // Object
console.log( getType( [] )); // Array
console.log( getType( new MyObject() )); // MyObject
var bTest = false,
uAny, // Is undefined
fTest function() {};
// Non constructed standard types
console.log( getType( bTest )); // Boolean
console.log( getType( 1.00 )); // Number
console.log( getType( 2000 )); // Number
console.log( getType( 'hello' )); // String
console.log( getType( "hello" )); // String
console.log( getType( fTest )); // Function
console.log( getType( uAny )); // false, cannot produce
// a string
Low cost and simple.

The best solution is toString (as stated above):
function getRealObjectType(obj: {}): string {
return Object.prototype.toString.call(obj).match(/\[\w+ (\w+)\]/)[1].toLowerCase();
}
FAIR WARNING: toString considers NaN a number so you must manually safeguard later with Number.isNaN(value).
The other solution suggested, using Object.getPrototypeOf fails with null and undefined

I put together a little type check utility inspired by the above correct answers:
thetypeof = function(name) {
let obj = {};
obj.object = 'object Object'
obj.array = 'object Array'
obj.string = 'object String'
obj.boolean = 'object Boolean'
obj.number = 'object Number'
obj.type = Object.prototype.toString.call(name).slice(1, -1)
obj.name = Object.prototype.toString.call(name).slice(8, -1)
obj.is = (ofType) => {
ofType = ofType.toLowerCase();
return (obj.type === obj[ofType])? true: false
}
obj.isnt = (ofType) => {
ofType = ofType.toLowerCase();
return (obj.type !== obj[ofType])? true: false
}
obj.error = (ofType) => {
throw new TypeError(`The type of ${name} is ${obj.name}: `
+`it should be of type ${ofType}`)
}
return obj;
};
example:
if (thetypeof(prop).isnt('String')) thetypeof(prop).error('String')
if (thetypeof(prop).is('Number')) // do something

How to Deep clone in javascript

How do you deep clone a JavaScript object?
I know there are various functions based on frameworks like JSON.parse(JSON.stringify(o)) and $.extend(true, {}, o) but I don't want to use a framework like that.
What is the most elegant or efficient way to create a deep clone.
We do care about edge cases like cloning array's. Not breaking prototype chains, dealing with self reference.
We don't care about supporting copying of DOM objects and like because .cloneNode exists for that reason.
As I mainly want to use deep clones in node.js using ES5 features of the V8 engine is acceptable.
[Edit]
Before anyone suggests let me mention there is a distinct difference between creating a copy by prototypically inheriting from the object and cloning it. The former makes a mess of the prototype chain.
[Further Edit]
After reading your answer I came to the annoying discovery that cloning entire objects is a very dangerous and difficult game. Take for example the following closure based object
var o = (function() {
var magic = 42;
var magicContainer = function() {
this.get = function() { return magic; };
this.set = function(i) { magic = i; };
}
return new magicContainer;
}());
var n = clone(o); // how to implement clone to support closures
Is there any way to write a clone function that clones the object, has the same state at time of cloning but cannot alter the state of o without writing a JS parser in JS.
There should be no real world need for such a function anymore. This is mere academic interest.

Very simple way, maybe too simple:
var cloned = JSON.parse(JSON.stringify(objectToClone));

It really depends what you would like to clone. Is this a truly JSON object or just any object in JavaScript? If you would like to do any clone, it might get you into some trouble. Which trouble? I will explain it below, but first, a code example which clones object literals, any primitives, arrays and DOM nodes.
function clone(item) {
if (!item) { return item; } // null, undefined values check
var types = [ Number, String, Boolean ],
result;
// normalizing primitives if someone did new String('aaa'), or new Number('444');
types.forEach(function(type) {
if (item instanceof type) {
result = type( item );
}
});
if (typeof result == "undefined") {
if (Object.prototype.toString.call( item ) === "[object Array]") {
result = [];
item.forEach(function(child, index, array) {
result[index] = clone( child );
});
} else if (typeof item == "object") {
// testing that this is DOM
if (item.nodeType && typeof item.cloneNode == "function") {
result = item.cloneNode( true );
} else if (!item.prototype) { // check that this is a literal
if (item instanceof Date) {
result = new Date(item);
} else {
// it is an object literal
result = {};
for (var i in item) {
result[i] = clone( item[i] );
}
}
} else {
// depending what you would like here,
// just keep the reference, or create new object
if (false && item.constructor) {
// would not advice to do that, reason? Read below
result = new item.constructor();
} else {
result = item;
}
}
} else {
result = item;
}
}
return result;
}
var copy = clone({
one : {
'one-one' : new String("hello"),
'one-two' : [
"one", "two", true, "four"
]
},
two : document.createElement("div"),
three : [
{
name : "three-one",
number : new Number("100"),
obj : new function() {
this.name = "Object test";
}
}
]
})
And now, let's talk about problems you might get when start cloning REAL objects. I'm talking now, about objects which you create by doing something like
var User = function(){}
var newuser = new User();
Of course you can clone them, it's not a problem, every object expose constructor property, and you can use it to clone objects, but it will not always work. You also can do simple for in on this objects, but it goes to the same direction - trouble. I have also included clone functionality inside the code, but it's excluded by if( false ) statement.
So, why cloning can be a pain? Well, first of all, every object/instance might have some state. You never can be sure that your objects doesn't have for example an private variables, and if this is the case, by cloning object, you just break the state.
Imagine there is no state, that's fine. Then we still have another problem. Cloning via "constructor" method will give us another obstacle. It's an arguments dependency. You never can be sure, that someone who created this object, did not did, some kind of
new User({
bike : someBikeInstance
});
If this is the case, you are out of luck, someBikeInstance was probably created in some context and that context is unkown for clone method.
So what to do? You still can do for in solution, and treat such objects like normal object literals, but maybe it's an idea not to clone such objects at all, and just pass the reference of this object?
Another solution is - you could set a convention that all objects which must be cloned should implement this part by themselves and provide appropriate API method ( like cloneObject ). Something what cloneNode is doing for DOM.
You decide.

The JSON.parse(JSON.stringify()) combination to deep copy Javascript objects is an ineffective hack, as it was meant for JSON data. It does not support values of undefined or function () {}, and will simply ignore them (or null them) when "stringifying" (marshalling) the Javascript object into JSON.
A better solution is to use a deep copy function. The function below deep copies objects, and does not require a 3rd party library (jQuery, LoDash, etc).
function copy(aObject) {
// Prevent undefined objects
// if (!aObject) return aObject;
let bObject = Array.isArray(aObject) ? [] : {};
let value;
for (const key in aObject) {
// Prevent self-references to parent object
// if (Object.is(aObject[key], aObject)) continue;
value = aObject[key];
bObject[key] = (typeof value === "object") ? copy(value) : value;
}
return bObject;
}
Note: This code can check for simple self-references (uncomment the section // Prevent self-references to parent object), but you should also avoid creating objects with self-references when possible. Please see: https://softwareengineering.stackexchange.com/questions/11856/whats-wrong-with-circular-references

There is now structuredClone in the Web API which also works with circular references.
Previous answer
Here is an ES6 function that will also work for objects with cyclic references:
function deepClone(obj, hash = new WeakMap()) {
if (Object(obj) !== obj) return obj; // primitives
if (hash.has(obj)) return hash.get(obj); // cyclic reference
const result = obj instanceof Set ? new Set(obj) // See note about this!
: obj instanceof Map ? new Map(Array.from(obj, ([key, val]) =>
[key, deepClone(val, hash)]))
: obj instanceof Date ? new Date(obj)
: obj instanceof RegExp ? new RegExp(obj.source, obj.flags)
// ... add here any specific treatment for other classes ...
// and finally a catch-all:
: obj.constructor ? new obj.constructor()
: Object.create(null);
hash.set(obj, result);
return Object.assign(result, ...Object.keys(obj).map(
key => ({ [key]: deepClone(obj[key], hash) }) ));
}
// Sample data
var p = {
data: 1,
children: [{
data: 2,
parent: null
}]
};
p.children[0].parent = p;
var q = deepClone(p);
console.log(q.children[0].parent.data); // 1
A note about Sets and Maps
How to deal with the keys of Sets and Maps is debatable: those keys are often primitives (in which case there is no debate), but they can also be objects. In that case the question becomes: should those keys be cloned?
One could argue that this should be done, so that if those objects are mutated in the copy, the objects in the original are not affected, and vice versa.
On the other hand one would want that if a Set/Map has a key, this should be true in both the original and the copy -- at least before any change is made to either of them. It would be strange if the copy would be a Set/Map that has keys that never occurred before (as they were created during the cloning process): surely that is not very useful for any code that needs to know whether a given object is a key in that Set/Map or not.
As you notice, I am more of the second opinion: the keys of Sets and Maps are values (maybe references) that should remain the same.
Such choices will often also surface with other (maybe custom) objects. There is no general solution, as much depends on how the cloned object is expected to behave in your specific case.

we can achieve deep clone by using structuredClone()
const original = { name: "stack overflow" };
// Clone it
const clone = structuredClone(original);

The Underscore.js contrib library library has a function called snapshot that deep clones an object
snippet from the source:
snapshot: function(obj) {
if(obj == null || typeof(obj) != 'object') {
return obj;
}
var temp = new obj.constructor();
for(var key in obj) {
if (obj.hasOwnProperty(key)) {
temp[key] = _.snapshot(obj[key]);
}
}
return temp;
}
once the library is linked to your project, invoke the function simply using
_.snapshot(object);

Lo-Dash, now a superset of Underscore.js, has a couple of deep clone functions:
_.cloneDeep(object)
_.cloneDeepWith(object, (val) => {if(_.isElement(val)) return val.cloneNode(true)})
the second parameter is a function that is invoked to produce the cloned value.
From an answer of the author himself:
lodash underscore build is provided to ensure compatibility with the latest stable version of Underscore.

As others have noted on this and similar questions, cloning an "object", in the general sense, is dubious in JavaScript.
However, there is a class of objects, which I call "data" objects, that is, those constructed simply from { ... } literals and/or simple property assignments or deserialized from JSON for which it is reasonable to want to clone. Just today I wanted to artificially inflate data received from a server by 5x to test what happens for a large data set, but the object (an array) and its children had to be distinct objects for things to function correctly. Cloning allowed me to do this to multiply my data set:
return dta.concat(clone(dta),clone(dta),clone(dta),clone(dta));
The other place I often end up cloning data objects is for submitting data back to the host where I want to strip state fields from the object in the data model before sending it. For example, I might want to strip all fields starting with "_" from the object as it is cloned.
This is the code I ended up writing to do this generically, including supporting arrays and a selector to choose which members to clone (which uses a "path" string to determine context):
function clone(obj,sel) {
return (obj ? _clone("",obj,sel) : obj);
}
function _clone(pth,src,sel) {
var ret=(src instanceof Array ? [] : {});
for(var key in src) {
if(!src.hasOwnProperty(key)) { continue; }
var val=src[key], sub;
if(sel) {
sub+=pth+"/"+key;
if(!sel(sub,key,val)) { continue; }
}
if(val && typeof(val)=='object') {
if (val instanceof Boolean) { val=Boolean(val); }
else if(val instanceof Number ) { val=Number (val); }
else if(val instanceof String ) { val=String (val); }
else { val=_clone(sub,val,sel); }
}
ret[key]=val;
}
return ret;
}
The simplest reasonable deep-clone solution, assuming a non-null root object and with no member selection is:
function clone(src) {
var ret=(src instanceof Array ? [] : {});
for(var key in src) {
if(!src.hasOwnProperty(key)) { continue; }
var val=src[key];
if(val && typeof(val)=='object') { val=clone(val); }
ret[key]=val;
}
return ret;
}

This is the deep cloning method I use, I think it
Great, hope you make suggestions
function deepClone (obj) {
var _out = new obj.constructor;
var getType = function (n) {
return Object.prototype.toString.call(n).slice(8, -1);
}
for (var _key in obj) {
if (obj.hasOwnProperty(_key)) {
_out[_key] = getType(obj[_key]) === 'Object' || getType(obj[_key]) === 'Array' ? deepClone(obj[_key]) : obj[_key];
}
}
return _out;
}

The below function is most efficient way to deep clone javascript objects.
function deepCopy(obj){
if (!obj || typeof obj !== "object") return obj;
var retObj = {};
for (var attr in obj){
var type = obj[attr];
switch(true){
case (type instanceof Date):
var _d = new Date();
_d.setDate(type.getDate())
retObj[attr]= _d;
break;
case (type instanceof Function):
retObj[attr]= obj[attr];
break;
case (type instanceof Array):
var _a =[];
for (var e of type){
//_a.push(e);
_a.push(deepCopy(e));
}
retObj[attr]= _a;
break;
case (type instanceof Object):
var _o ={};
for (var e in type){
//_o[e] = type[e];
_o[e] = deepCopy(type[e]);
}
retObj[attr]= _o;
break;
default:
retObj[attr]= obj[attr];
}
}
return retObj;
}
var obj = {
string: 'test',
array: ['1'],
date: new Date(),
object:{c: 2, d:{e: 3}},
function: function(){
return this.date;
}
};
var copyObj = deepCopy(obj);
console.log('object comparison', copyObj === obj); //false
console.log('string check', copyObj.string === obj.string); //true
console.log('array check', copyObj.array === obj.array); //false
console.log('date check', copyObj2.date === obj.date); //false
console.log('object check', copyObj.object === obj.object); //false
console.log('function check', copyObj.function() === obj.function()); //true

Avoid use this method
let cloned = JSON.parse(JSON.stringify(objectToClone));
Why? this method will convert 'function,undefined' to null
const myObj = [undefined, null, function () {}, {}, '', true, false, 0, Symbol];
const IsDeepClone = JSON.parse(JSON.stringify(myObj));
console.log(IsDeepClone); //[null, null, null, {…}, "", true, false, 0, null]
try to use deepClone function.There are several above

There should be no real world need for such a function anymore. This is mere academic interest.
As purely an exercise, this is a more functional way of doing it. It's an extension of #tfmontague's answer as I'd suggested adding a guard block there. But seeing as I feel compelled to ES6 and functionalise all the things, here's my pimped version. It complicates the logic as you have to map over the array and reduce over the object, but it avoids any mutations.
const cloner = (x) => {
const recurseObj = x => (typeof x === 'object') ? cloner(x) : x
const cloneObj = (y, k) => {
y[k] = recurseObj(x[k])
return y
}
// Guard blocks
// Add extra for Date / RegExp if you want
if (!x) {
return x
}
if (Array.isArray(x)) {
return x.map(recurseObj)
}
return Object.keys(x).reduce(cloneObj, {})
}
const tests = [
null,
[],
{},
[1,2,3],
[1,2,3, null],
[1,2,3, null, {}],
[new Date('2001-01-01')], // FAIL doesn't work with Date
{x:'', y: {yx: 'zz', yy: null}, z: [1,2,3,null]},
{
obj : new function() {
this.name = "Object test";
}
} // FAIL doesn't handle functions
]
tests.map((x,i) => console.log(i, cloner(x)))

my addition to all the answers
function deepCopy(arr) {
if (typeof arr !== 'object') return arr
if (Array.isArray(arr)) return [...arr].map(deepCopy)
for (const prop in arr)
copy[prop] = deepCopy(arr[prop])
return copy
}

My solution, deep clones objects, arrays and functions.
let superClone = (object) => {
let cloning = {};
Object.keys(object).map(prop => {
if(Array.isArray(object[prop])) {
cloning[prop] = [].concat(object[prop])
} else if(typeof object[prop] === 'object') {
cloning[prop] = superClone(object[prop])
} else cloning[prop] = object[prop]
})
return cloning
}
example
let obj = {
a: 'a',
b: 'b',
c: {
deep: 'try and copy me',
d: {
deeper: 'try me again',
callDeeper() {
return this.deeper
}
},
arr: [1, 2, 3]
},
hi() {
return this.a
}
};
const cloned = superClone(obj)
obj.a = 'A'
obj.c.deep = 'i changed'
obj.c.arr = [45,454]
obj.c.d.deeper = 'i changed'
console.log(cloned) // unchanged object
If your objects contain methods don't use JSON to deep clone, JSON deep cloning doesn't clone methods.
If you take a look at this, object person2 only clones the name, not person1's greet method.
const person1 = {
name: 'John',
greet() {
return `HI, ${this.name}`
}
}
const person2 = JSON.parse(JSON.stringify(person1))
console.log(person2) // { name: 'John' }

Deep cloning of the object can be done in several ways but each having their own limitations as mentioned below. Hence, I will suggest you to use structuredClone algorithm.
JSON.parse(JSON.stringify(object)) - won't copy functions, Dates, undefineds & many more.
const obj = {
name: 'alpha',
printName: function() {
console.log(this.name);
}
};
console.log(JSON.parse(JSON.stringify(obj))); // function not copied
_.cloneDeep(object) - It is a good option but requires lodash.
const obj = {
name: 'alpha',
printName: function() {
console.log(this.name);
}
};
filteredArray = _.cloneDeep(obj);
console.log(filteredArray)
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/1.2.1/lodash.min.js"></script>
structuredClone(object) - Browser Native API (It is good to use as JSON.parse() and JSON.stringify() do not serialize the circular object or things like Map, Set, Date, RegEx etc.)
const a = { x: 20, date: new Date() };
a.c = a;
console.log(structuredClone(a)); // { x: 20, date: <date object>, c: <circular ref> }
console.log(JSON.parse(JSON.stringify(a))); // throwing a TypeError

I noticed that Map should require special treatment, thus with all suggestions in this thread, code will be:
function deepClone( obj ) {
if( !obj || true == obj ) //this also handles boolean as true and false
return obj;
var objType = typeof( obj );
if( "number" == objType || "string" == objType ) // add your immutables here
return obj;
var result = Array.isArray( obj ) ? [] : !obj.constructor ? {} : new obj.constructor();
if( obj instanceof Map )
for( var key of obj.keys() )
result.set( key, deepClone( obj.get( key ) ) );
for( var key in obj )
if( obj.hasOwnProperty( key ) )
result[key] = deepClone( obj[ key ] );
return result;
}

This works for arrays, objects and primitives. Doubly recursive algorithm that switches between two traversal methods:
const deepClone = (objOrArray) => {
const copyArray = (arr) => {
let arrayResult = [];
arr.forEach(el => {
arrayResult.push(cloneObjOrArray(el));
});
return arrayResult;
}
const copyObj = (obj) => {
let objResult = {};
for (key in obj) {
if (obj.hasOwnProperty(key)) {
objResult[key] = cloneObjOrArray(obj[key]);
}
}
return objResult;
}
const cloneObjOrArray = (el) => {
if (Array.isArray(el)) {
return copyArray(el);
} else if (typeof el === 'object') {
return copyObj(el);
} else {
return el;
}
}
return cloneObjOrArray(objOrArray);
}

We can utilize recursion for making deepCopy. It can create copy of array, object, array of object, object with function.
if you want, you can add function for other type of data structure like map etc.
function deepClone(obj) {
var retObj;
_assignProps = function(obj, keyIndex, retObj) {
var subType = Object.prototype.toString.call(obj[keyIndex]);
if(subType === "[object Object]" || subType === "[object Array]") {
retObj[keyIndex] = deepClone(obj[keyIndex]);
}
else {
retObj[keyIndex] = obj[keyIndex];
}
};
if(Object.prototype.toString.call(obj) === "[object Object]") {
retObj = {};
for(key in obj) {
this._assignProps(obj, key, retObj);
}
}
else if(Object.prototype.toString.call(obj) == "[object Array]") {
retObj = [];
for(var i = 0; i< obj.length; i++) {
this._assignProps(obj, i, retObj);
}
};
return retObj;
};

Use immutableJS
import { fromJS } from 'immutable';
// An object we want to clone
let objA = {
a: { deep: 'value1', moreDeep: {key: 'value2'} }
};
let immB = fromJS(objA); // Create immutable Map
let objB = immB.toJS(); // Convert to plain JS object
console.log(objA); // Object { a: { deep: 'value1', moreDeep: {key: 'value2'} } }
console.log(objB); // Object { a: { deep: 'value1', moreDeep: {key: 'value2'} } }
// objA and objB are equalent, but now they and their inner objects are undependent
console.log(objA === objB); // false
console.log(objA.a === objB.a); // false
console.log(objA.moreDeep === objB.moreDeep); // false
Or lodash/merge
import merge from 'lodash/merge'
var objA = {
a: [{ 'b': 2 }, { 'd': 4 }]
};
// New deeply cloned object:
merge({}, objA );
// We can also create new object from several objects by deep merge:
var objB = {
a: [{ 'c': 3 }, { 'e': 5 }]
};
merge({}, objA , objB ); // Object { a: [{ 'b': 2, 'c': 3 }, { 'd': 4, 'e': 5 }] }

This one, using circular reference, works for me
//a test-object with circular reference :
var n1 = { id:0, text:"aaaaa", parent:undefined}
var n2 = { id:1, text:"zzzzz", parent:undefined }
var o = { arr:[n1,n2], parent:undefined }
n1.parent = n2.parent = o;
var obj = { a:1, b:2, o:o }
o.parent = obj;
function deepClone(o,output){
if(!output) output = {};
if(o.______clone) return o.______clone;
o.______clone = output.______clone = output;
for(var z in o){
var obj = o[z];
if(typeof(obj) == "object") output[z] = deepClone(obj)
else output[z] = obj;
}
return output;
}
console.log(deepClone(obj));

var newDate = new Date(this.oldDate);
I was passing oldDate to function and generating newDate from this.oldDate, but it was changing this.oldDate also.So i used that solution and it worked.

This solution will avoid recursion problems when using [...target] or {...target}
function shallowClone(target) {
if (typeof a == 'array') return [...target]
if (typeof a == 'object') return {...target}
return target
}
/* set skipRecursion to avoid throwing an exception on recursive references */
/* no need to specify refs, or path -- they are used interally */
function deepClone(target, skipRecursion, refs, path) {
if (!refs) refs = []
if (!path) path = ''
if (refs.indexOf(target) > -1) {
if (skipRecursion) return null
throw('Recursive reference at ' + path)
}
refs.push(target)
let clone = shallowCopy(target)
for (i in target) target[i] = deepClone(target, refs, path + '.' + i)
return clone
}

Hello i just wanted to post my answer since i think its more readable. Note:this doesnt cover classes since i dont use them but you can easily add a condition for that
/** Copies any type of object/array of objects
* #param obj The object to be copied
* #param customKeys A list of keys that are to be excluded from deepCopy (optional)
*/
export function deepCopyObject(obj: any, customKeys?: Array<string|number|symbol>) {
if (obj == undefined)
return;
if (typeof obj !== 'object')
return obj;
if (typeof obj === 'function')
return obj;
const isArray = obj.length > -1;
if (isArray)
return copyArray(obj);
const isObjectDate = obj instanceof Date;
if(isObjectDate)
return new Date(obj);
const isDOM = obj.nodeType && typeof obj.cloneNode == "function";
if (isDOM)
return obj.cloneNode(true);
const isHtmlComponent = obj.$$typeof != undefined; // you can pass html/react components and maybe setup a custom function to copy them
if (isHtmlComponent)
return obj;
const newObject = <typeof obj>{};
const keys = Object.keys(obj);
keys.forEach((key: keyof (typeof obj)) => {
newObject[key] = copyKeysOfTypeObject(obj, key, customKeys);
})
const cantAccessObjectKeys = keys.lenght ==0; // ex: window.navigator
if (cantAccessObjectKeys)
return obj;
return newObject
}
function copyArray(arr: any) {
const newArr = new Array(0);
arr.forEach((obj: any) => {
newArr.push(deepCopyObject(obj));
})
return newArr;
}
function copyKeysOfTypeObject(obj: any, key: string | number | symbol, customKeys?: Array<string | number | symbol>) {
if (!key)
return;
if (customKeys && customKeys.includes(key))
return obj[key];
return deepCopyObject(obj[key]);
}

structuredClone now is supported by most the browsers
its main limitation is about DONT coping functions. It would require some extra work to copy/move it manually.
We can at least copy classes in an easy way by adding the prototypes later
const proto = Object.getPrototypeOf(object)
const newObject = structuredClone(object)
Object.setPrototypeOf(newObject, proto)

let obj1 = {
a: 100,
b: {
c: 200,
d: [1, 2, 3],
e: () => {}
}
}
function deepClone(obj) {
let newObj = {};
for (let key in obj) {
let val = obj[key];
if (val instanceof Array) {
newObj[key] = [...val]
} else if (typeof val === 'object') {
newObj[key] = deepClone(val)
} else {
newObj[key] = val;
}
}
return newObj;
}
obj2 = deepClone(obj1);
obj1.b.c = 300;
console.log(obj1);
console.log(obj2);