Unexpected behavior in JSON.parse Reviver function, deleting the object and not the key properties

Unexpected behavior in JSON.parse Reviver function, deleting the object and not the key properties

By : Steve Lambert
Date : November 20 2020, 11:01 PM
hope this fix your issue Your second example left return value; off.
But even tough you did that, it should only have removed the properties that returned undefined as value, and I think you found a bug (may be?).
code :
if (name == "") {
  return value;
obj = {
   one: 1,
   innerObj: {
     two: 2,
     four: 4
   two: 2,
   three: 3,
   four: 4
b = {};
json = JSON.stringify(obj);

* This does not work as expected, instead of deleting the property on the object, the entire object returns undefined.
b = JSON.parse(json, function (name, value) {
  if (value % 2 === 0) {
    return -value;
  if (name == "") {
    return value;
// { two: -2, four: -4 }

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JSON.parse reviver function has n+1 keys?

JSON.parse reviver function has n+1 keys?

By : Mohammad Mohsin
Date : March 29 2020, 07:55 AM
I wish this helpful for you I wanted to test the code overload which can provide a reviver function when parsing a JSON string. , The answer is in the link you provided...
JSON.parse using reviver function

JSON.parse using reviver function

By : valerieann Bawn
Date : March 29 2020, 07:55 AM
Hope this helps After checking for the special case(s), you simply need to pass back unmodified values by default:
code :
var myObj = new Object();
myObj.firstname = "mike";
myObj.lastname = "smith";

var jsonString = JSON.stringify(myObj);
var jsonObj = JSON.parse(jsonString, dataReviver);

function dataReviver(key, value)
    if(key == 'lastname')
        var newLastname = "test";
        return newLastname;

  return value;  // < here is where un-modified key/value pass though


JSON.stringify(jsonObj )// "{"firstname":"mike","lastname":"test"}" 
JSON.parse with reviver parameter to whitelist object fields

JSON.parse with reviver parameter to whitelist object fields

By : Sudi
Date : March 29 2020, 07:55 AM
I wish this helpful for you The reviver callback is called for each property of the JSON object, including nested properties, and finally for the object itself. So the last call of the reviver callback will get key = '' and value = [the JSON object] as arguments. '' is not equal to 'a', so your reviver callback returns undefined when it is called for the last time for the whole object. This is why you see undefined for your "whitelisting" approach.
Another problem will arise when you use your approach on nested objects:
code :
var test = "{\"a\": { \"a\": \"A\", \"d\": \"D\" }, \"b\": \"B\", \"c\": \"C\"}";

console.log(JSON.parse(test, function(key, val){ if (key === "a" || key === "") return val; }));
//  { a: { a: 'A' } }  <-- property d is missing
var whitelist = ['a'];
for (var prop in jsonObject) {
    if (!jsonObject.hasOwnProperty(prop)) continue;
    if (whitelist.indexOf(prop) === -1) delete jsonObject[prop];
How do I use `JSON.parse`'s reviver function to add data to each object in an array?

How do I use `JSON.parse`'s reviver function to add data to each object in an array?

By : Aurélie Leportier
Date : March 29 2020, 07:55 AM
I wish this helpful for you You don't need to create a new object. The map function, if used correctly, will return a new array(with new objects). And you can use the index provided by map to get your id.
code :
var musicList = {
  "files": [
          "title": "Ironic"
          "title": "It's Beginning To Look A Lot Like Christmas"
          "title": "Sweet Dreams"

var stringifiedMusic = JSON.stringify(musicList);

var parsedMusic = JSON.parse(stringifiedMusic, function(key, value) {

  if (key === 'files') {
    return value.map(function (item, index) {
      item.id = index;
      return item;
  return value;

console.log("parsedMusic", parsedMusic)
What is the problem with this JSON.parse reviver function?

What is the problem with this JSON.parse reviver function?

By : John Cosker
Date : March 29 2020, 07:55 AM
it fixes the issue The last call to reviver will happen with an empty string as the key "", which allows you to apply a transformation to the final object (in your case, you're transforming it to undefined). If you add a test for the empty string then it works properly:
code :
const whitelist = ['prop1', 'prop2', 'result'];
const reviver = (key, value) => {
  if (whitelist.includes(key) || key === '') {
    return value;
  } else {
    return undefined; // explicitly delete the entry

const theMightyJsonString = '{ "result": { "prop1": "Greetings", "prop2": "Hello", "prop3": "WASSUP!!!!" } }';

console.log( JSON.parse( theMightyJsonString, reviver ) );
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