How can I print a circular structure in a JSON-like format?

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')

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) and there is no need to try JSON.stringify each element in the chain leading to a circular reference.

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.

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());

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);

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}

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()) // [{},{}] ✅ )