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Save Console.log output to variable [duplicate]

I have a big object I want to convert to JSON and send. However it has circular structure, so if I try to use JSON.stringify() I'll get:
TypeError: Converting circular structure to JSON
or
TypeError: cyclic object value
I want to toss whatever circular references exist and send whatever can be stringified. How do I do that?
Thanks.
var obj = {
a: "foo",
b: obj
}
I want to stringify obj into:
{"a":"foo"}

In Node.js, you can use util.inspect(object). It automatically replaces circular links with "[Circular]".
Albeit being built-in (no installation is required), you must import it
import * as util from 'util' // has no default export
import { inspect } from 'util' // or directly
// or
var util = require('util')
To use it, simply call
console.log(util.inspect(myObject))
Also be aware that you can pass options object to inspect (see link above)
inspect(myObject[, options: {showHidden, depth, colors, showProxy, ...moreOptions}])
Please, read and give kudos to commenters below...

Use JSON.stringify with a custom replacer. For example:
// Demo: Circular reference
var circ = {};
circ.circ = circ;
// Note: cache should not be re-used by repeated calls to JSON.stringify.
var cache = [];
JSON.stringify(circ, (key, value) => {
if (typeof value === 'object' && value !== null) {
// Duplicate reference found, discard key
if (cache.includes(value)) return;
// Store value in our collection
cache.push(value);
}
return value;
});
cache = null; // Enable garbage collection
The replacer in this example is not 100% correct (depending on your definition of "duplicate"). In the following case, a value is discarded:
var a = {b:1}
var o = {};
o.one = a;
o.two = a;
// one and two point to the same object, but two is discarded:
JSON.stringify(o, ...);
But the concept stands: Use a custom replacer, and keep track of the parsed object values.
As a utility function written in es6:
// safely handles circular references
JSON.safeStringify = (obj, indent = 2) => {
let cache = [];
const retVal = JSON.stringify(
obj,
(key, value) =>
typeof value === "object" && value !== null
? cache.includes(value)
? undefined // Duplicate reference found, discard key
: cache.push(value) && value // Store value in our collection
: value,
indent
);
cache = null;
return retVal;
};
// Example:
console.log('options', JSON.safeStringify(options))

I wonder why nobody posted the proper solution from MDN page yet...
const circularReference = {otherData: 123};
circularReference.myself = circularReference;
const getCircularReplacer = () => {
const seen = new WeakSet();
return (key, value) => {
if (typeof value === "object" && value !== null) {
if (seen.has(value)) {
return;
}
seen.add(value);
}
return value;
};
};
const stringified = JSON.stringify(circularReference, getCircularReplacer());
console.log(stringified);
Seen values should be stored in a set, not in array (replacer gets called on every element).
Like in the accepted answer, this solution removes all repeating values, not just the circular ones. But at least it does not have exponential complexity.

just do
npm i --save circular-json
then in your js file
const CircularJSON = require('circular-json');
...
const json = CircularJSON.stringify(obj);
https://github.com/WebReflection/circular-json
NOTE: I have nothing to do with this package. But I do use it for this.
Update 2020
Please note CircularJSON is in maintenance only and flatted is its successor.

I really liked Trindaz's solution - more verbose, however it had some bugs. I fixed them for whoever likes it too.
Plus, I added a length limit on my cache objects.
If the object I am printing is really big - I mean infinitely big - I want to limit my algorithm.
JSON.stringifyOnce = function(obj, replacer, indent){
var printedObjects = [];
var printedObjectKeys = [];
function printOnceReplacer(key, value){
if ( printedObjects.length > 2000){ // browsers will not print more than 20K, I don't see the point to allow 2K.. algorithm will not be fast anyway if we have too many objects
return 'object too long';
}
var printedObjIndex = false;
printedObjects.forEach(function(obj, index){
if(obj===value){
printedObjIndex = index;
}
});
if ( key == ''){ //root element
printedObjects.push(obj);
printedObjectKeys.push("root");
return value;
}
else if(printedObjIndex+"" != "false" && typeof(value)=="object"){
if ( printedObjectKeys[printedObjIndex] == "root"){
return "(pointer to root)";
}else{
return "(see " + ((!!value && !!value.constructor) ? value.constructor.name.toLowerCase() : typeof(value)) + " with key " + printedObjectKeys[printedObjIndex] + ")";
}
}else{
var qualifiedKey = key || "(empty key)";
printedObjects.push(value);
printedObjectKeys.push(qualifiedKey);
if(replacer){
return replacer(key, value);
}else{
return value;
}
}
}
return JSON.stringify(obj, printOnceReplacer, indent);
};

Note that there is also a JSON.decycle method implemented by Douglas Crockford. See his
cycle.js. This allows you to stringify almost any standard structure:
var a = [];
a[0] = a;
a[1] = 123;
console.log(JSON.stringify(JSON.decycle(a)));
// result: '[{"$ref":"$"},123]'.
You can also recreate original object with retrocycle method. So you don't have to remove cycles from objects to stringify them.
However this will not work for DOM Nodes (which are typical cause of cycles in real life use-cases). For example this will throw:
var a = [document.body];
console.log(JSON.stringify(JSON.decycle(a)));
I've made a fork to solve that problem (see my cycle.js fork). This should work fine:
var a = [document.body];
console.log(JSON.stringify(JSON.decycle(a, true)));
Note that in my fork JSON.decycle(variable) works as in the original and will throw an exception when the variable contain DOM nodes/elements.
When you use JSON.decycle(variable, true) you accept the fact that the result will not be reversible (retrocycle will not re-create DOM nodes). DOM elements should be identifiable to some extent though. For example if a div element has an id then it will be replaced with a string "div#id-of-the-element".

#RobW's answer is correct, but this is more performant ! Because it uses a hashmap/set:
const customStringify = function (v) {
const cache = new Set();
return JSON.stringify(v, function (key, value) {
if (typeof value === 'object' && value !== null) {
if (cache.has(value)) {
// Circular reference found
try {
// If this value does not reference a parent it can be deduped
return JSON.parse(JSON.stringify(value));
}
catch (err) {
// discard key if value cannot be deduped
return;
}
}
// Store value in our set
cache.add(value);
}
return value;
});
};

I'd recommend checking out json-stringify-safe from #isaacs-- it's used in NPM.
BTW- if you're not using Node.js, you can just copy and paste lines 4-27 from the relevant part of the source code.
To install:
$ npm install json-stringify-safe --save
To use:
// Require the thing
var stringify = require('json-stringify-safe');
// Take some nasty circular object
var theBigNasty = {
a: "foo",
b: theBigNasty
};
// Then clean it up a little bit
var sanitized = JSON.parse(stringify(theBigNasty));
This yields:
{
a: 'foo',
b: '[Circular]'
}
Note that, just like with the vanilla JSON.stringify function as #Rob W mentioned, you can also customize the sanitization behavior by passing in a "replacer" function as the second argument to stringify(). If you find yourself needing a simple example of how to do this, I just wrote a custom replacer which coerces errors, regexps, and functions into human-readable strings here.

For future googlers searching for a solution to this problem when you don't know the keys of all circular references, you could use a wrapper around the JSON.stringify function to rule out circular references. See an example script at https://gist.github.com/4653128.
The solution essentially boils down to keeping a reference to previously printed objects in an array, and checking that in a replacer function before returning a value. It's more constrictive than only ruling out circular references, because it also rules out ever printing an object twice, one of the side affects of which is to avoid circular references.
Example wrapper:
function stringifyOnce(obj, replacer, indent){
var printedObjects = [];
var printedObjectKeys = [];
function printOnceReplacer(key, value){
var printedObjIndex = false;
printedObjects.forEach(function(obj, index){
if(obj===value){
printedObjIndex = index;
}
});
if(printedObjIndex && typeof(value)=="object"){
return "(see " + value.constructor.name.toLowerCase() + " with key " + printedObjectKeys[printedObjIndex] + ")";
}else{
var qualifiedKey = key || "(empty key)";
printedObjects.push(value);
printedObjectKeys.push(qualifiedKey);
if(replacer){
return replacer(key, value);
}else{
return value;
}
}
}
return JSON.stringify(obj, printOnceReplacer, indent);
}

var a={b:"b"};
a.a=a;
JSON.stringify(preventCircularJson(a));
evaluates to:
"{"b":"b","a":"CIRCULAR_REFERENCE_REMOVED"}"
with the function:
/**
* Traverses a javascript object, and deletes all circular values
* #param source object to remove circular references from
* #param censoredMessage optional: what to put instead of censored values
* #param censorTheseItems should be kept null, used in recursion
* #returns {undefined}
*/
function preventCircularJson(source, censoredMessage, censorTheseItems) {
//init recursive value if this is the first call
censorTheseItems = censorTheseItems || [source];
//default if none is specified
censoredMessage = censoredMessage || "CIRCULAR_REFERENCE_REMOVED";
//values that have allready apeared will be placed here:
var recursiveItems = {};
//initaite a censored clone to return back
var ret = {};
//traverse the object:
for (var key in source) {
var value = source[key]
if (typeof value == "object") {
//re-examine all complex children again later:
recursiveItems[key] = value;
} else {
//simple values copied as is
ret[key] = value;
}
}
//create list of values to censor:
var censorChildItems = [];
for (var key in recursiveItems) {
var value = source[key];
//all complex child objects should not apear again in children:
censorChildItems.push(value);
}
//censor all circular values
for (var key in recursiveItems) {
var value = source[key];
var censored = false;
censorTheseItems.forEach(function (item) {
if (item === value) {
censored = true;
}
});
if (censored) {
//change circular values to this
value = censoredMessage;
} else {
//recursion:
value = preventCircularJson(value, censoredMessage, censorChildItems.concat(censorTheseItems));
}
ret[key] = value
}
return ret;
}

Use the JSON.stringify method with a replacer. Read this documentation for more information. http://msdn.microsoft.com/en-us/library/cc836459%28v=vs.94%29.aspx
var obj = {
a: "foo",
b: obj
}
var replacement = {"b":undefined};
alert(JSON.stringify(obj,replacement));
Figure out a way to populate the replacement array with cyclic references. You can use the typeof method to find if an the property is of type 'object' ( reference ) and an exact equality check ( === ) to verify circular reference.

If
console.log(JSON.stringify(object));
results in a
TypeError: cyclic object value
Then you may want to print like this:
var output = '';
for (property in object) {
output += property + ': ' + object[property]+'; ';
}
console.log(output);

I know this is an old question, but I'd like to suggest an NPM package I've created called smart-circular, which works differently from the other ways proposed. It's specially useful if you're using big and deep objects.
Some features are:
Replacing circular references or simply repeated structures inside the object by the path leading to its first occurrence (not just the string [circular]);
By looking for circularities in a breadth-first search, the package ensures this path is as small as possible, which is important when dealing with very big and deep objects, where the paths can get annoyingly long and difficult to follow (the custom replacement in JSON.stringify does a DFS);
Allows personalised replacements, handy to simplify or ignore less important parts of the object;
Finally, the paths are written exactly in the way necessary to access the field referenced, which can help you debugging.

The second argument to JSON.stringify() also allows you to specify an array of key names that should be preserved from every object it encounters within your data. This may not work for all use cases, but is a much simpler solution.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
var obj = {
a: "foo",
b: this
}
var json = JSON.stringify(obj, ['a']);
console.log(json);
// {"a":"foo"}
Note: Strangely, the object definition from OP does not throw a circular reference error in the latest Chrome or Firefox. The definition in this answer was modified so that it did throw an error.

I found circular-json library on github and it worked well for my problem.
Some good features I found useful:
Supports multi-platform usage but I only tested it with node.js so far.
API is same so all you need to do is include and use it as a JSON replacement.
It have it's own parsing method so you can convert the 'circular' serialized data back to object.

To update the answer of overriding the way JSON works (probably not recommended, but super simple), don't use circular-json (it's deprecated). Instead, use the successor, flatted:
https://www.npmjs.com/package/flatted
Borrowed from the old answer above from #user1541685 , but replaced with the new one:
npm i --save flatted
then in your js file
const CircularJSON = require('flatted');
const json = CircularJSON.stringify(obj);

This code will fail for circular reference:
JSON.stringify(circularReference);
// TypeError: cyclic object value
Use the below code:
const getCircularReplacer = () => {
const seen = new WeakSet();
return (key, value) => {
if (typeof value === "object" && value !== null) {
if (seen.has(value)) {
return;
}
seen.add(value);
}
return value;
};
};
JSON.stringify(circularReference, getCircularReplacer());

This solution fixes the issue reported by user2451227 on accepted answer (when o = {}; JSON.stringify([o, o], getCircularReplacer())).
function newCircularReplacer () {
const seenValues = []
return circularReplacer
function circularReplacer (key, value) {
if (typeof value === 'object' && value !== null && Object.keys(value).length) {
const stackSize= seenValues.length
if (stackSize) {
for (let n = stackSize - 1; seenValues[n][key] !== value; --n)
seenValues.pop() // clean up expired references
if (seenValues.includes(value)) return '[Circular]'
}
seenValues.push(value)
}
return value
}
}
let o = {a: 1}
o.b = o // Circular reference
console.log(
JSON.stringify(o, newCircularReplacer()) // {a:1,b:[Circular]} ✅
)
o = {}
a = [o, o] // NOT circular reference
console.log(
JSON.stringify(a, newCircularReplacer()) // [{},{}] ✅
)

I resolve this problem like this:
var util = require('util');
// Our circular object
var obj = {foo: {bar: null}, a:{a:{a:{a:{a:{a:{a:{hi: 'Yo!'}}}}}}}};
obj.foo.bar = obj;
// Generate almost valid JS object definition code (typeof string)
var str = util.inspect(b, {depth: null});
// Fix code to the valid state (in this example it is not required, but my object was huge and complex, and I needed this for my case)
str = str
.replace(/<Buffer[ \w\.]+>/ig, '"buffer"')
.replace(/\[Function]/ig, 'function(){}')
.replace(/\[Circular]/ig, '"Circular"')
.replace(/\{ \[Function: ([\w]+)]/ig, '{ $1: function $1 () {},')
.replace(/\[Function: ([\w]+)]/ig, 'function $1(){}')
.replace(/(\w+): ([\w :]+GMT\+[\w \(\)]+),/ig, '$1: new Date("$2"),')
.replace(/(\S+): ,/ig, '$1: null,');
// Create function to eval stringifyed code
var foo = new Function('return ' + str + ';');
// And have fun
console.log(JSON.stringify(foo(), null, 4));

Try this:
var obj = {
a: "foo",
b: obj
};
var circular_replacer = (value) => {
var seen = [];
if (value != null && typeof value == "object") {
if (seen.indexOf(value) >= 0) return;
seen.push(value);
}
return value;
};
obj = circular_replacer(obj);

Although this has been answered sufficiently, you could also explicitly delete the property in question before stringification using the delete operator.
delete obj.b;
const jsonObject = JSON.stringify(obj);
delete operator
this will remove the need to build or maintain complex logic to remove circular references.

function myStringify(obj, maxDeepLevel = 2) {
if (obj === null) {
return 'null';
}
if (obj === undefined) {
return 'undefined';
}
if (maxDeepLevel < 0 || typeof obj !== 'object') {
return obj.toString();
}
return Object
.entries(obj)
.map(x => x[0] + ': ' + myStringify(x[1], maxDeepLevel - 1))
.join('\r\n');
}

Most of the answers in this thread are catered to use with JSON.stringify specifically -- they do not show how to actually remove circular-references in the original object-tree. (well, short of calling JSON.parse again afterward -- which requires reassignment, and has a higher performance impact)
For removing circular-references from the source object-tree, you can use a function such as this: https://stackoverflow.com/a/63952549/2441655
These general-purpose circular-reference-remover functions can then be used to make subsequent calls to circular-reference-sensitive functions (like JSON.stringify) safe:
const objTree = {normalProp: true};
objTree.selfReference = objTree;
RemoveCircularLinks(objTree); // without this line, the JSON.stringify call errors
console.log(JSON.stringify(objTree));

Here's a solution that:
removes cycles only (and not all duplicate object references, as do most of the solutions posted here so far),
is not unnecessarily verbose,
is fast,
does not require any library dependency.
function replaceCycles(obj, replacement = undefined, seen = new WeakSet()) {
if (typeof obj === 'object')
if (seen.has(obj))
return replacement
else {
seen.add(obj)
const newObj = {}
for (const key in obj)
newObj[key] = replaceCycles(obj[key], replacement, seen)
seen.delete(obj)
return newObj
}
else
return obj
}
Usage:
const a = {
b: 'v1',
c: {
d: 'v2'
}
}
a.e = a.c
a.c.f = a.c
console.log(JSON.stringify(replaceCycles(a, '[CYCLE]')))
Output:
"{'b':'v1','c':{'d':'v2','f':'[CYCLE]'},'e':{'d':'v2','f':'[CYCLE]'}}"

an other solution for resolving this issue with these kind of objects is that using this library
https://github.com/ericmuyser/stringy
its simple and you can in a few simple step solve this.

Based on the other answers I end up with the following code. It works pretty well with circular references, objects with custom constructors.
From the given object to be serialized,
Cache all the object you come across while traversing the object and assign each of them a unique hashID (an auto-incrementing number also works)
Once a circular reference is found mark that field in the new object as circular and store the hashID of the original object as an attribute.
Github Link - DecycledJSON
DJSHelper = {};
DJSHelper.Cache = [];
DJSHelper.currentHashID = 0;
DJSHelper.ReviveCache = [];
// DOES NOT SERIALIZE FUNCTION
function DJSNode(name, object, isRoot){
this.name = name;
// [ATTRIBUTES] contains the primitive fields of the Node
this.attributes = {};
// [CHILDREN] contains the Object/Typed fields of the Node
// All [CHILDREN] must be of type [DJSNode]
this.children = []; //Array of DJSNodes only
// If [IS-ROOT] is true reset the Cache and currentHashId
// before encoding
isRoot = typeof isRoot === 'undefined'? true:isRoot;
this.isRoot = isRoot;
if(isRoot){
DJSHelper.Cache = [];
DJSHelper.currentHashID = 0;
// CACHE THE ROOT
object.hashID = DJSHelper.currentHashID++;
DJSHelper.Cache.push(object);
}
for(var a in object){
if(object.hasOwnProperty(a)){
var val = object[a];
if (typeof val === 'object') {
// IF OBJECT OR NULL REF.
/***************************************************************************/
// DO NOT REMOVE THE [FALSE] AS THAT WOULD RESET THE [DJSHELPER.CACHE]
// AND THE RESULT WOULD BE STACK OVERFLOW
/***************************************************************************/
if(val !== null) {
if (DJSHelper.Cache.indexOf(val) === -1) {
// VAL NOT IN CACHE
// ADD THE VAL TO CACHE FIRST -> BEFORE DOING RECURSION
val.hashID = DJSHelper.currentHashID++;
//console.log("Assigned", val.hashID, "to", a);
DJSHelper.Cache.push(val);
if (!(val instanceof Array)) {
// VAL NOT AN [ARRAY]
try {
this.children.push(new DJSNode(a, val, false));
} catch (err) {
console.log(err.message, a);
throw err;
}
} else {
// VAL IS AN [ARRAY]
var node = new DJSNode(a, {
array: true,
hashID: val.hashID // HashID of array
}, false);
val.forEach(function (elem, index) {
node.children.push(new DJSNode("elem", {val: elem}, false));
});
this.children.push(node);
}
} else {
// VAL IN CACHE
// ADD A CYCLIC NODE WITH HASH-ID
this.children.push(new DJSNode(a, {
cyclic: true,
hashID: val.hashID
}, false));
}
}else{
// PUT NULL AS AN ATTRIBUTE
this.attributes[a] = 'null';
}
} else if (typeof val !== 'function') {
// MUST BE A PRIMITIVE
// ADD IT AS AN ATTRIBUTE
this.attributes[a] = val;
}
}
}
if(isRoot){
DJSHelper.Cache = null;
}
this.constructorName = object.constructor.name;
}
DJSNode.Revive = function (xmlNode, isRoot) {
// Default value of [isRoot] is True
isRoot = typeof isRoot === 'undefined'?true: isRoot;
var root;
if(isRoot){
DJSHelper.ReviveCache = []; //Garbage Collect
}
if(window[xmlNode.constructorName].toString().indexOf('[native code]') > -1 ) {
// yep, native in the browser
if(xmlNode.constructorName == 'Object'){
root = {};
}else{
return null;
}
}else {
eval('root = new ' + xmlNode.constructorName + "()");
}
//CACHE ROOT INTO REVIVE-CACHE
DJSHelper.ReviveCache[xmlNode.attributes.hashID] = root;
for(var k in xmlNode.attributes){
// PRIMITIVE OR NULL REF FIELDS
if(xmlNode.attributes.hasOwnProperty(k)) {
var a = xmlNode.attributes[k];
if(a == 'null'){
root[k] = null;
}else {
root[k] = a;
}
}
}
xmlNode.children.forEach(function (value) {
// Each children is an [DJSNode]
// [Array]s are stored as [DJSNode] with an positive Array attribute
// So is value
if(value.attributes.array){
// ITS AN [ARRAY]
root[value.name] = [];
value.children.forEach(function (elem) {
root[value.name].push(elem.attributes.val);
});
//console.log("Caching", value.attributes.hashID);
DJSHelper.ReviveCache[value.attributes.hashID] = root[value.name];
}else if(!value.attributes.cyclic){
// ITS AN [OBJECT]
root[value.name] = DJSNode.Revive(value, false);
//console.log("Caching", value.attributes.hashID);
DJSHelper.ReviveCache[value.attributes.hashID] = root[value.name];
}
});
// [SEPARATE ITERATION] TO MAKE SURE ALL POSSIBLE
// [CYCLIC] REFERENCES ARE CACHED PROPERLY
xmlNode.children.forEach(function (value) {
// Each children is an [DJSNode]
// [Array]s are stored as [DJSNode] with an positive Array attribute
// So is value
if(value.attributes.cyclic){
// ITS AND [CYCLIC] REFERENCE
root[value.name] = DJSHelper.ReviveCache[value.attributes.hashID];
}
});
if(isRoot){
DJSHelper.ReviveCache = null; //Garbage Collect
}
return root;
};
DecycledJSON = {};
DecycledJSON.stringify = function (obj) {
return JSON.stringify(new DJSNode("root", obj));
};
DecycledJSON.parse = function (json, replacerObject) {
// use the replacerObject to get the null values
return DJSNode.Revive(JSON.parse(json));
};
DJS = DecycledJSON;
Example Usage 1:
var obj = {
id:201,
box: {
owner: null,
key: 'storm'
},
lines:[
'item1',
23
]
};
console.log(obj); // ORIGINAL
// SERIALIZE AND THEN PARSE
var jsonObj = DJS.stringify(obj);
console.log(DJS.parse(jsonObj));
Example Usage 2:
// PERSON OBJECT
function Person() {
this.name = null;
this.child = null;
this.dad = null;
this.mom = null;
}
var Dad = new Person();
Dad.name = 'John';
var Mom = new Person();
Mom.name = 'Sarah';
var Child = new Person();
Child.name = 'Kiddo';
Dad.child = Mom.child = Child;
Child.dad = Dad;
Child.mom = Mom;
console.log(Child); // ORIGINAL
// SERIALIZE AND THEN PARSE
var jsonChild = DJS.stringify(Child);
console.log(DJS.parse(jsonChild));

I know this question is old and has lots of great answers but I post this answer because of it's new flavor (es5+)
Object.defineProperties(JSON, {
refStringify: {
value: function(obj) {
let objMap = new Map();
let stringified = JSON.stringify(obj,
function(key, value) {
// only for objects
if (typeof value == 'object') {
// If has the value then return a reference to it
if (objMap.has(value))
return objMap.get(value);
objMap.set(value, `ref${objMap.size + 1}`);
}
return value;
});
return stringified;
}
},
refParse: {
value: function(str) {
let parsed = JSON.parse(str);
let objMap = _createObjectMap(parsed);
objMap.forEach((value, key) => _replaceKeyWithObject(value, key));
return parsed;
}
},
});
// *************************** Example
let a = {
b: 32,
c: {
get a() {
return a;
},
get c() {
return a.c;
}
}
};
let stringified = JSON.refStringify(a);
let parsed = JSON.refParse(stringified, 2);
console.log(parsed, JSON.refStringify(parsed));
// *************************** /Example
// *************************** Helper
function _createObjectMap(obj) {
let objMap = new Map();
JSON.stringify(obj, (key, value) => {
if (typeof value == 'object') {
if (objMap.has(value))
return objMap.get(value);
objMap.set(value, `ref${objMap.size + 1}`);
}
return value;
});
return objMap;
}
function _replaceKeyWithObject(key, obj, replaceWithObject = obj) {
Object.keys(obj).forEach(k => {
let val = obj[k];
if (val == key)
return (obj[k] = replaceWithObject);
if (typeof val == 'object' && val != replaceWithObject)
_replaceKeyWithObject(key, val, replaceWithObject);
});
}

You could try the JSON parser library: treedoc. it supports circular references and also dedupes the repeated objects with references.
yarn add treedoc
import {TD} from 'treedoc'
TD.stringify(obj);
If you want more customization
import {TD, TDEncodeOption} from 'treedoc'
const opt = new TDEncodeOption();
opt.coderOption.setShowType(true).setShowFunction(true);
opt.jsonOption.setIndentFactor(2);
return TD.stringify(obj, opt);
The generated JSON file can be viewed by the viewer http://treedoc.org, which supports the navigation through JSON node references.
[shameless plug] I'm the author of this library

I created following method for my LoggingUtilities class.
Following method takes source and target objects, and assign source to target by given maxLevel.
static assignObjectByLevel(
sourceObject: any,
targetObject: any,
currentLevel: number = 0,
maxLevel: number = 3,
showUndefinedValues = false
): any {
if (currentLevel >= maxLevel) {
return;
}
const objQueue = [];
for (const key in sourceObject) {
if (sourceObject.hasOwnProperty(key)) {
const value = sourceObject[key];
if (typeof value === "object") {
objQueue.push({ key, value });
} else {
targetObject[key] = value;
}
} else {
if (showUndefinedValues) {
targetObject[key] = "undefined/null";
}
}
}
while (objQueue.length > 0) {
const objVal = objQueue.pop();
currentLevel++;
targetObject[objVal.key] = {};
this.assignObjectByLevel(
objVal.value,
targetObject[objVal.key],
currentLevel,
maxLevel,
false
);
}
}
Usage Example:
const logObjParam = {
level1: "value1",
level2: {
value2: "value2",
level3: {
value3: "value3",
level4: {
value4: " value4",
level5: {
value5: " value5",
},
},
},
},
};
let logObj = {};
this.assignObjectByLevel(logObjParam, logObj);
Result:
{
"level1": "value1",
"level2": {
"value2": "value2",
"level3": {
"value3": "value3",
"level4": {}
}
}
}

superserial fully serializes JavaScript objects.
https://github.com/denostack/superserial
Usage:
const serializer = new Serializer();
const nodes = [{ self: null as any, siblings: [] as any[] }, {
self: null as any,
siblings: [] as any[],
}];
nodes[0].self = nodes[0];
nodes[0].siblings = nodes;
nodes[1].self = nodes[1];
nodes[1].siblings = nodes;
const serialized = serializer.serialize(nodes);
console.log(serialized);
output:
[$1,$2];{"self":$1,"siblings":$0};{"self":$2,"siblings":$0}

How to prevent object to add duplicate value and stop excuting function

Hey guys i am adding data to the array as object but i wanted to if there is any duplicate item code so its stop excuting the function and return and if the the condition is true so its take the constructor value and add itno the data structure
This what i try to prevent it from adding the value but its not work as i want
function getNo(b){
for (const [key, value] of Object.entries(data)) {
let val = value.itemCode;
if(b === val){
alert('Its equalt to item code');
break;}else{ return b;};
}}
----What i want is-----
1) Check if value is duplicate or not from the itemCode constructor
2)If its a duplicate value so its should show and alert and stop excuting the function
3)And add this function into the addItem function to check its duplicate or not
4)I store value in the data array
var item = function(name,itemCode,stock){
this.name = name;
this.itemCode = itemCode;
this.stock = stock;
}
var data = [];
function addItem(name,itemCode,stock){
var Newitem = new item(name,itemCode,stock);
data.push(Newitem);
}
addItem('BlueTee',100,50);
addItem('Yellow tee',101,100);
addItem('BrownTee',102,120);

There are multiple ways to handle this. Your choice should depend on other use cases.
The easiest way is to define data as a javascript object instead of an array. This would require keys for each object. This would look like this:
var data = {};
function addItem(name, itemCode, stock){
var newItem = new item(name, itemCode, stock);
if(data[itemCode] === undefined)
data[itemCode] = newItem;
}
If you are going to later access data as an array, then you can instead iterate over the array for each insertion. This would look like this:
function addItem(name, itemCode, stock){
var newItem = new item(name, itemCode, stock);
if(!data.some(function(x => x.itemCode === itemCode)){
data.push(newItem);
}
}
This would be slower than a normal insertion especially for large datasets. If you are going to use a very large dataset and need to be able to access as an array, then I would use a hybrid between the two. The javascript object would be used for direct access to the object. A class-like implementation would be preferred for that, but without using oo, the code would look something like this:
var data = [];
var keys = {};
function addItem(name, itemCode, stock){
var newItem = new item(name, itemCode, stock);
if(keys[itemCode] === undefined){
data.push(newItem);
keys[itemCode] = data.length - 1;
}
}
This implementation also gets complicated if you are going to modify the array more than just adding elements

You can map the data array to itemCodes and see if it includes the itemCode of the new item, and if so return an empty object for your constructor. Then in your addItem function you can choose not to add the object to the array if the object is empty.
var item = function(name,itemCode,stock){
if (data.map(i => i.itemCode).includes(itemCode)) {
alert("This item has a duplicate itemCode");
return this;
}
this.name = name;
this.itemCode = itemCode;
this.stock = stock;
}
var data = [];
function addItem(name,itemCode,stock){
var Newitem = new item(name,itemCode,stock);
if (Newitem.name) data.push(Newitem); // check if an object was created with properties
}
addItem('BlueTee',100,50);
addItem('Yellow tee',101,100);
addItem('BrownTee',102,120);
addItem('RedTee',100,70); // this won't be added because of duplicate itemCode
console.log(data); // only contains BlueTee, Yellow tee, and BrownTee objects

Why Javascript object didn't change?

Can someone explain me this strange js behavior ?
All of this is in AngularJS.
I have helper function in my main app.js to simply return element from an array by its id:
var MyLib = MyLib || {};
MyLib.helpers = {
find: function(needle, stack) {
for (var i = 0; i < stack.length; i++) {
if(stack[i]._id === needle)
return stack[i];
}
return false;
}
}
Then I have factory and function to handle database change:
// categories are grabbed from db
var categories = [some array of objects];
// change is object returned from database that has all info about object as well as new object itself
function handleChange(change) {
var _category = MyLib.helpers.find(change.id, categories);
// if deleted, that part is ok
if(change.deleted) {
var idx = categories.indexOf(_category);
if(idx !== -1) {
categories.splice(idx, 1);
}
} else {
// if updated that part is weird
if(_category) {
_category = change.doc;
}
// if newly added that part is ok
else {
categories.push( angular.copy(change.doc) );
}
}
}
Why when I try to update element grabbed from categories array doesn't update in categories array ?
// categories ARE NOT updated after this
_category = change.doc;
and only when I refer to categories by index like this:
// categories ARE updated after this although _category is returned from this array by index (find function)
var idx = categories.indexOf(_category);
categories[idx] = change.doc;
I don't understand this...

You are overwriting the variable with a new value and any reference to prior value is gone.
Instead of overwriting the original object value with a new object you could update the existing object using angular.extend()
angular.extend(_category, change.doc);

I didn't analyze everything, but you should always have dot notation.
_category pass by value, and will not change when 'MyLib.hel ...' is changed
var _category = MyLib.helpers.find(change.id, categories);
something.category pass by reference, and will be changed when 'MyLib.hel ...' is changed
var something.category = MyLib.helpers.find(change.id, categories);

By using array.push method elements are getting added but it's overriding last object as well

I'm facing an weird issue here every time I am pushing obj to the array arrays length is increasing as expected but the object which I am push at last that is overriding all other object, I am not able to identify my mistake so please help me. Thanks in Advance please check following code.
var tablehead = {};
var experimentsData = [];
var obj = {};
var remoteSheet = response.result.values;
remoteSheet.filter(function(innerArrayItem) {
if (i == 0) {
tablehead = innerArrayItem;
i++;
} else {
$.each(tablehead, function(key, value) {
obj[value] = innerArrayItem[key];
});
experimentsData.push(obj);
}
});

Because you're pushing the same object everytime. obj is only created once and at each iteration you override data you put in it at the previous iteration.
var experimentsData = [];
// var obj = {}; <-- don't define obj here
var remoteSheet = response.result.values;
remoteSheet.filter(function(innerArrayItem) {
if (i == 0) {
tablehead = innerArrayItem;
i++;
} else {
var obj = {} // <-- define it here
$.each(tablehead, function(key, value) {
obj[value] = innerArrayItem[key];
});
experimentsData.push(obj);
}
});
Also, filter is a bad way of iterating an array, I recommend switching to a basic for loop.

Get last value inserted into a Set

The MDN documentation for Set says that JavaScript Set objects retain insertion order of elements:
Set objects are collections of values, you can iterate its elements in insertion order.
Is there a way to get the last item inserted into a Set object?
var s = new Set();
s.add("Alpha");
s.add("Zeta");
s.add("Beta");
console.log(getLastItem(s)); // prints "Beta"
Edit
It is possible to implement a Linked Set datastructure container class that has the same interface as Set and has the desired capability. See my answer below.

I was not able to find any method to get last value inserted in set from ECMA 2015 Specification, may be they never intended such a method, but you can do something like:
const a = new Set([1, 2, 3]);
a.add(10);
const lastValue = Array.from(a).pop();
Edit:
on second thought, a space efficient solution might be:
function getLastValue(set){
let value;
for(value of set);
return value;
}
const a = new Set([1, 2, 3]);
a.add(10);
console.log('last value: ', getLastValue(a));

Some ideas:
Consider using an array instead of a set. Extracting the last element of an array is easy, e.g.
array[array.length-1];
array.slice(-1)[0];
array.pop(); // <-- This alters the array
If you really need a set, you can convert it to an array when you want to extract the last item, but that will cost time and space.
Iterate the set manually. This will cost time but not as much space as copying into an array. For example (there are probably more elegant ways to do this)
var set = new Set([1, 2, 3]);
var iter = set.values(), prev, curr;
do {
prev = curr;
curr = iter.next();
} while(!curr.done)
var last = prev.value; // 3
Consider inserting the items in reverse order. Then you only need to get the first item in the set, and that's easier:
set.values().next().value;
Subclass Set to add this new functionality:
class MySet extends Set {
add(value) {
super.add(value);
this.last = value;
}
}
var set = new MySet();
set.add(1); set.add(2); set.add(3);
set.last; // 3
Note this will only detect values added with add. To be more complete, it should also detect the latest value when the set is constructed, and update the value when the last item is removed.

Yes, there is a way to do that, you can simply convert the set to an array and pop of the last item
function getLastItem(_set) {
return [..._set].pop();
}
to get keys/values etc, you can do
return [..._set.entries()].pop(); // the entire entry
return [..._set.keys()].pop(); // the key only
return [..._set.values()].pop(); // the value only
If you don't want to create an array, you'd probably have to iterate and get the last value, like this
var last; s.forEach(k => { last = k }); // last === "Beta"
FIDDLE

Just another approach.
Set.prototype.last = function(){
return new Set().add( [...this].pop() );
}
Set.prototype.lastKey = function(){
return [...this.keys()].pop();
}
Set.prototype.lastValue = function(){
return [...this.values()].pop();
}
var lastSet = s.last(); // "Beta"
var lastKey = s.lastKey(); // "Beta"
var lastValue = s.lastValue(); // "Beta"

I have created a replacement for Set, which re-implements the linked functionality of the set, using an underlying Map.
class LinkedSetLink {
constructor(value) {
this.value = value;
this.prev = this;
this.next = this;
}
insertBefore(item) {
const prev = item.prev = this.prev;
const next = item.next = this;
next.prev = item;
prev.next = item;
}
remove() {
const prev = this.prev;
const next = this.next;
next.prev = prev;
prev.next = next;
}
}
class LinkedSet {
constructor(iterable) {
this._map = new Map();
this._pivot = new LinkedSetLink(/* undefined */);
if (iterable) {
this._addAll(iterable);
}
}
_addAll(iterable) {
for (const item of iterable) {
this.add(item);
}
}
has(item) {
return this._map.has(item);
}
add(item) {
if (!this._map.has(item)) {
const link = new LinkedSetLink(item);
this._pivot.insertBefore(link);
this._map.set(item, link);
}
}
delete(item) {
const link = this._map.get(item);
if (link) {
this._map.delete(item);
link.remove();
}
}
clear() {
this._map.clear();
this._pivot.next = this._pivot.prev = this._pivot;
}
get size() {
return this._map.size;
}
values() {
return this._map.keys();
}
keys() {
return this.values();
}
[Symbol.iterator]() {
return this.values();
}
*entries() {
for (const key of this.values()) {
yield [key, key];
}
}
first() {
return this._pivot.next.value;
}
last() {
return this._pivot.prev.value;
}
}
function test1() {
console.log(Array.from(new LinkedSet(["a", "b", "c"]).entries()));
}
function test2() {
console.log(new LinkedSet(["a", "b", "c"]).last());
}
<button onclick="test1()">test entries</button>
<button onclick="test2()">test last</button>

There is no method for accessing the last item, but you can do it as follows
let setOfNumbers = new Set([10]);
setOfNumbers.add(20).add(2);
let lastValue = [...setOfNumbers].pop()

A simple solution, but O(N):
const getLastValueFromSet = (set) => {
for (var value of set);
return value;
}