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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}

Constructing a DOMTokenList/DOMSettableTokenList instance

The DOMTokenList and DOMSettableTokenList interfaces (MDN, WHATWG) provide methods for manipulating ordered sets of string tokens represented by space-delimited strings. They are most commonly used in the form of the Element.prototype.classList property, a DOMTokenList which reflects the class attribute of an associated element.
var div = document.createElement('div');
div.setAttribute('class', 'hello world goodnight moon');
var list = div.classList;
console.assert(list.length === 4);
console.assert(list[0] === 'hello');
console.assert(list.item(1) === 'world');
console.assert(list.contains('moon') === true);
console.assert(list.contains('mars') === false);
list.remove('world', 'earth', 'dirt', 'sand');
list.add('hello', 'mars');
list.toggle('goodnight');
console.assert(div.getAttribute('class') === 'hello moon mars');
I'm working on a custom element (HTML5Rocks, W3C Draft) which displays a real-time feed of the activity of specified Stack Overflow users. This list of users is specified in an ids attribute, and may be updated at any time.
<so-users ids="1114 22656 106224"></so-users>
document.querySelector('so-users').setAttribute('ids', '23354 115866');
Instead of requiring users to manipulate this attribute directly, I would like to have an .ids property providing a DOMTokenList that they can use instead. Ideally this would be directly associated with the attribute, but an unbound DOMSettableTokenList instance that I have to manually bind would also be fine.
document.querySelector('so-users').ids.add('17174');
Unfortunately, I have been unable to find any way to create a DOMTokenList instance. The definition is not a constructor, and directly creating an object using its prototype results in errors when I call any associated methods:
new DOMTokenList; // TypeError: Illegal constructor
new DOMSettableTokenList; // TypeError: Illegal constructor
var list = Object.create(DOMSettableTokenList.prototype, {
value: { value: 'hello world' }
});
console.assert(list instanceof DOMTokenList);
console.assert(list instanceof DOMSettableTokenList);
list.item(0); // TypeError: Illegal invocation
function TokenListConstructor() {
this.value = 'hello world';
}
TokenListConstructor.prototype = DOMSettableTokenList.prototype;
var list = new TokenListConstructor;
console.assert(list instanceof DOMTokenList);
console.assert(list instanceof DOMSettableTokenList);
list.add('moon'); // TypeError: Illegal invocation
How can I construct a new DOMTokenList or DOMSettableTokenList instance?

You cannot create an DOMTokenList or an DOMSettableTokenList directly. Instead you should use the class attribute to store and retrieve your data and perhaps map an ids attribute of your DOM element to the classList property.
var element = document.querySelector('so-users');
element.ids = element.classList;
You can use relList according to the documentation but classList is more supported, the only drawback is that you might run into issues if one of your ids matches a class name so set an inline style to hide the element just in case.
For a custom component compatibility should be a concern (classList is present in IE>=10, Firefox 3.6, Chrome 8, Opera 11.5 and Safari 5.1, see http://caniuse.com/#feat=classlist) so if compatibility is in your requirements use the another solution posted below.
If you cannot use clases or classList and/or must use the ids attribute you should implement a custom function according to the spec with the following properties as functions.
item()
contains()
add()
remove()
toggle()
This is an example implementation of such functionality.
var TokenList = function (ids) {
'use strict';
var idsArray = [],
self = this,
parse = function (id, functionName, cb) {
var search = id.toString();
if (search.split(' ').length > 1) {
throw new Error("Failed to execute '" + functionName + "' on 'TokenList': The token provided ('" + search + "') contains HTML space characters, which are not valid in tokens.');");
} else {
cb(search);
}
};
function triggerAttributeChange() {
if (self.tokenChanged && typeof self.tokenChanged === 'function') {
self.tokenChanged(idsArray.toString());
}
}
if (ids && typeof ids === 'string') {
idsArray = ids.split(' ');
}
self.item = function (index) {
return idsArray[index];
};
self.contains = function (id) {
parse(id, 'contains', function (search) {
return idsArray.indexOf(search) !== -1;
});
};
self.add = function (id) {
parse(id, 'add', function (search) {
if (idsArray.indexOf(search) === -1) {
idsArray.push(search);
}
triggerAttributeChange();
});
};
self.remove = function (id) {
parse(id, 'remove', function (search) {
idsArray = idsArray.filter(function (item) {
return item !== id;
});
triggerAttributeChange();
});
};
self.toggle = function (id) {
parse(id, 'toggle', function (search) {
if (!self.contains(search)) {
self.add(search);
} else {
self.remove(search);
}
});
};
self.tokenChanged = null;
self.toString = function () {
var tokens = '',
i;
if (idsArray.length > 0) {
for (i = 0; i < idsArray.length; i = i + 1) {
tokens = tokens + idsArray[i] + ' ';
}
tokens = tokens.slice(0, tokens.length - 1);
}
return tokens;
};
};
Set an 'ids' property in your element with a new instance of this function and finally you must bound the targeted attribute to the property listening to changes to the element and updating the property o viceversa. You can do that with a mutation observer.
See firing event on DOM attribute change and https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver
var attachTokenList = function (element, prop, initialValues) {
'use strict';
var initValues = initialValues || element.getAttribute(prop),
MutationObserver = window.MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver,
observer,
config,
cancelMutation = false;
function createTokenList(values) {
var tList = new TokenList(values);
tList.tokenChanged = function () {
element.setAttribute(prop, element[prop].toString());
cancelMutation = true;
};
element[prop] = tList;
}
createTokenList(initValues);
observer = new MutationObserver(function (mutation) {
var i,
mutationrec,
newAttr;
if (mutation.length > 0 && !cancelMutation) {
for (i = 0; i < mutation.length; i = i + 1) {
mutationrec = mutation[i];
if (mutationrec.attributeName === prop && element[prop]) {
newAttr = element.getAttribute(prop);
createTokenList(newAttr);
}
}
}
cancelMutation = false;
});
config = {
attributes: true
};
observer.observe(element, config);
};
Testing to see if it works
<so-users ids="1234 5678"></so-users>
<button onclick="clickButton1()">Add 7890</button>
<button onclick="clickButton2()">Set to 3456</button>
<button onclick="clickButton3()">Add 9876</button>
Inside a script tag
var elem = document.querySelector('so-users');
attachTokenList(elem, 'ids')
function clickButton1 () {
elem.ids.add('7890');
}
function clickButton2 () {
elem.setAttribute('ids', '3456');
}
function clickButton3 () {
elem.ids.add('9876');
}
Clicking the buttons in sequence set the ids attribute to '3456 9876'

You can get an instance of DOMTokenList with this function:
function newDOMTokenList(initialTokens) {
const tmp = document.createElement(`div`);
const classList = tmp.classList;
if (initialTokens) {
initialTokens.forEach(token => {
classList.add(token);
});
}
return classList;
}
We can 'steal' the DOMTokenList from a div, since it does not affect the current document until you choose to insert the element (for example by using insertAdjacentElement) and it will be garbage collected since we do not keep any references to the variable tmp.
Then you can use your list:
var list = newDOMTokenList(['a', 'b']);
list.add('c');
list.contains('d'); // false
list.contains('b'); // true
list.item(1) // 'b'
list instanceof DOMTokenList // true
// etc...
// render it to a string
var soUsers = document.querySelector('so-users');
soUsers.setAttribute('ids', list.toString());
You can even add a MutationObserver to the tmp element and get callbacks whenever the classList changes:
function newDOMTokenList(initialTokens, changed) {
const tmp = document.createElement('div');
const classList = tmp.classList;
if (initialTokens) {
initialTokens.forEach(token => {
classList.add(token);
});
}
if (changed) {
const observer = new MutationObserver((mutationList, observer) => {
for (const mutation of mutationList) {
if (mutation.attributeName === 'class') {
changed();
}
}
});
observer.observe(tmp, {attributes: true});
}
return classList;
}
This, however, will cause the tmp div to never be garbage collected, since the MutationObserver needs to keep a reference to it.

Utilizing Custom Elements - Adding JS properties and methods initialization approach , HTMLElement.dataset
, try
var XFooProto = Object.create(HTMLElement.prototype);
// 1. Give x-foo a foo() method.
XFooProto.contains = function(id) {
var data = JSON.parse(this.dataset.ids);
return data.some(function(_id) {
return id == _id
})
};
XFooProto.add = function(id) {
var data = JSON.parse(this.dataset.ids);
if (!this.contains(id)) {
data.push(id);
};
return data
};
XFooProto.remove = function(id) {
var data = JSON.parse(this.dataset.ids);
if (this.contains(id)) {
for (var _id in data) {
if (data[_id] === id) {
data.splice(_id, 1)
}
};
};
return data
};
XFooProto.ids = function() {
return this.dataset.ids
};
// 2. Define a property read-only "bar".
// Object.defineProperty(XFooProto, "ids", {value: this});
// 3. Register x-foo's definition.
var XFoo = document.registerElement('x-foo', {prototype: XFooProto});
// 4. Instantiate an x-foo.
var xfoo = document.createElement('x-foo');
xfoo.dataset.ids = '["23354", "115866"]';
// 5. Add it to the page.
document.body.appendChild(xfoo);
console.log(xfoo.add("123")); // `["23354", "115866", "123"]`
console.log(xfoo.remove("123")); // `["23354", "115866"]`
console.log(xfoo.contains("123")); // `false`
console.log(xfoo.contains("23354")); // `true`
console.log(xfoo.ids()); // `["23354", "115866"]` , type : `String`
var pre = document.getElementsByTagName("pre")[0]
pre.innerText = JSON.stringify(JSON.parse(xfoo.dataset.ids), null, 4);
<pre></pre>

new Object with prototype function vs regular function which returns an object

The basic idea is to check if it starts with an underscore and if there is split the string and return whatever comes after the underscore. This function will be run many times, but for different strings, it is unlikely i will need to retrieve the information more than once for each stirng.
A simple function which will return an object with the data I need:
var parseElementName = function(i) {
var sliced = [i.slice(0, 1), i.slice(1, i.length)];
var obj = {
isClass: null,
name: ''
}
if(sliced[0] === '_') {
obj.name = sliced[1];
obj.isClass = true;
} else {
obj.name = i;
obj.isClass = false;
}
return obj
}
Called with parseElementName(i);
Object with prototyped function
var parsedElement = function(i) {
this.className =
this.isClass = null;
if(this.setElementName(i))
return true
}
parsedElement.prototype.setElementName = function(i) {
var sliced = [i.slice(0, 1), i.slice(1, i.length)];
if(sliced[0] === '_') {
this.className = sliced[1];
this.isClass = true
} else {
this.className = i;
this.isClass = false
}
}
Called with var parsed_element = new parsedElement();
then parsed_element.className or parsedElement.isClass
Which approach is recommended?

I like the object prototype approach best, but I have a few notes about your code:
Use semicolons at the end of each line
Class names should be capitalized. So it should be ParsedElement
I wouldn't call it className, because it is confusing when it is not a class, I would rename it name

The two ways have different outcomes - that constructor+prototype approach will yield an instance which has a setElementName method. Will you ever need this to change the fields of an existing object? It's a simple parser function, so I would assume no. In that case, you should go with returning the object literal:
function parseElementName(i) {
var isClass = i.charAt(0) == '_';
return {
isClass: isClass,
name = isClass ? i.slice(1) : i
};
}
If you really need that method later, consider #MaxMeier's and #HMR's points.

animating css transformations with javascript

I have a specific problem and general question.
I have to animate dragging with javascript (no frameworks), and I think it's better to use translate() instead of changing top and left, at least for better perfomance.
But it is part of user-driven interface, so I can't predefine any animation. So I have to build a string with updated values and assign it to element style property.
It's my problem.
So if I have to animate a few user-driven transformations I have to do relatively heavy string operations to update necessary values and keep those which I don't animate? Is there any kind of simpler API to do it with javascript?
I want to understand it at first, so no frameworks, please.
Thanks.

I saw Ilya's comment about matrices, which is probably a good thing to check out. Given I am struggled at matrix math, a string based solution is right up my alley.
I threw this together in about half an hour but it seems to work well. I assume you'll just capture mouse move and update the translate value. I created the toObject method in case you wanted to do some more advanced animations.
I think if you're going to go this route, you should reconsider not wanting to use frameworks.
(function() {
var setTransFunc, getTransFunc;
// make sure cross browser...
// I don't know if this is nescessary. Every browser I tried worked on the first options.
(function () {
var testElem = document.createElement('DIV');
if (testElem.style.transform !== undefined) {
setTransFunc = function (elem, str) {
elem.style.transform = str;
}
getTransFunc = function (elem) {
return elem.style.transform;
}
}
else if (testElem.style.webkitTransform !== undefined) {
setTransFunc = function (elem, str) {
elem.style.webkitTransform = str;
}
getTransFunc = function (elem) {
return elem.style.webkitTransform;
}
}
else if (testElem.style.msTransform !== undefined) {
setTransFunc = function (elem, str) {
elem.style.msTransform = str;
}
getTransFunc = function (elem) {
return elem.style.msTransform;
}
}
else {
throw ('unable to detect set/get methods for transform style.');
}
}).call();
// constructor
var _tranZ = function (elem) {
this.elem = (typeof elem == 'string') ? document.getElementById(elem) : elem;
};
(function () {
this.elem = null;
// sets transform style
this.set = function (str) {
setTransFunc(this.elem, str);
return this;
}
// gets string of transform style
this.get = function () {
return getTransFunc(this.elem);
}
// adds a trasnform
this.add = function (str) {
this.set(this.get() + ' ' + str);
return this;
}
// removes a transform
this.remove = function (name) {
var re = new RegExp(name + "\\([^)]*\\)", "gi");
console.log(re);
this.set(this.get().replace(re, ""));
return this;
}
// represent transforms as object. Might be easier later on to animate with this.
this.getTransformObject = function () {
var str = this.get(),
re = /(\w+)\s*\(([^)]*)\)/g,
match, obj = {};
while (match = re.exec(str)) {
obj[match[1]] = {
parameters: match[2].split(/\s*,\s*/)
}
}
return obj;
}
}).call(_tranZ.prototype);
// add a window module
window.tranZ = function (elem) {
return new _tranZ(elem);
};
})();
jsFiddle

More efficient Javascript

Looking for another eye on making the following Javascript more efficient.
The following JSON is produced from a Resteasy service:
var testing = {
"com:klistret:cmdb:ci:pojo:successful":true,
"com:klistret:cmdb:ci:pojo:count":1,
"com:klistret:cmdb:ci:pojo:elements":{
"com:klistret:cmdb:ci:pojo:id":123,
"com:klistret:cmdb:ci:pojo:name":"Mars",
"com:klistret:cmdb:ci:pojo:type":{
"com:klistret:cmdb:ci:pojo:id":1,
"com:klistret:cmdb:ci:pojo:name":"Environment"
},
"com:klistret:cmdb:ci:pojo:configuration":{
"#www:w3:org:2001:XMLSchemainstance:type":"Environment",
"#Watermark":"past",
"com:klistret:cmdb:ci:commons:Name":"Mars"
}
}
};
Extended the Extjs JSONReader to handle key depths higher than 2 in the createAccessor method. Wondering if there is a way to make the code more efficient? The function below will be called like function(testing, "com:klistret:cmdb:ci:pojo:configuration.#Watermark") where the com:klistret:cmdb:ci:pojo:elements property is the root.
createAccessor : function(){
var re = /[\[\.]/;
return function(expr) {
if(Ext.isEmpty(expr)){
return Ext.emptyFn;
}
if(Ext.isFunction(expr)){
return expr;
}
# THIS FUNCTION I WANT TO BE EFFICIENT
return function(obj){
while (String(expr).search(re) !== -1) {
var i = String(expr).search(re);
var key = expr.substring(0, i);
if (obj.hasOwnProperty(key)) {
obj = obj[key];
}
expr = expr.substring(i+1, expr.length);
}
return obj[expr];
};
};
}()

This is what I use. I only allow dot annotation, mind:
Ext.override(Ext.data.JsonReader, {
createAccessor: function() {
return function(expr) {
if (Ext.isEmpty(expr)) {
return Ext.emptyFn;
} else if (Ext.isFunction(expr)) {
return expr;
} else {
return function(obj) {
var parts = (expr || '').split('.'),
result = obj,
part,
match;
while (parts.length > 0 && result) {
part = parts.shift();
match = part.match(/^(.+?)(\[(\d+)\])?$/);
result = result[match[1]];
if (result && match[3]) {
result = result[match[3]];
}
}
return result;
}
}
};
}()
});

A basic optimization would be to avoid scanning the string twice with search, which is pretty slow.
The best you could do is replace all the string scanning and substring extraction with a single call to expr.split('.'), which would support accessors of the form aaa.bbb.ccc.ddd and turn them into an array like ['aaa','bbb','ccc','ddd']. The other two characters you seem to support ([ and ]) wouldn't work.
Alternately, you could do an initial match for /[^\].[]+/g over your entire string and keep the matches to obtain a similar array, but this would possibly be slower than the previous solution.