TypeError: Converting circular structure to JSON in nodejs

I also ran into this issue. It was because I forgot to await for a promise.

I was able to get the values using this method, found at careerkarma.com

Output looks like this.

I just run this code in the debugger console. Pass your object to this function.
Copy paste the function also.

 const replacerFunc = () => {
    const visited = new WeakSet();
    return (key, value) => {
      if (typeof value === "object" && value !== null) {
        if (visited.has(value)) {
          return;
        }
        visited.add(value);
      }
      return value;
    };
  };
  
  JSON.stringify(circObj, replacerFunc());

Try using this npm package. This helped me decoding the res structure from my node while using passport-azure-ad for integrating login using Microsoft account

https://www.npmjs.com/package/circular-json

You can stringify your circular structure by doing:

const str = CircularJSON.stringify(obj);

then you can convert it onto JSON using JSON parser

JSON.parse(str)

I forgotten to use await keyword in async function. with the given systax

blogRouter.put('/:id', async (request, response) => {
  const updatedBlog = Blog.findByIdAndUpdate(
    request.params.id,
    request.body,
    { new: true }
  );
  response.status(201).json(updatedBlog);
});

Blog.findByIdAndUpdate should be used with the await keyword.

use this https://www.npmjs.com/package/json-stringify-safe

var stringify = require('json-stringify-safe');
var circularObj = {};
circularObj.circularRef = circularObj;
circularObj.list = [ circularObj, circularObj ];
console.log(stringify(circularObj, null, 2));


stringify(obj, serializer, indent, decycler)

If you are sending reponse , Just use await before response

await res.json({data: req.data});

It's because you don't an async response For example:

app.get(`${api}/users`, async (req, res) => {
    const users = await User.find()
    res.send(users);
   })

I was also getting the same error, in my case it was just because of not using await with Users.findById() which returns promise, so response.status().send()/response.send() was getting called before promise is settled (fulfilled or rejected)

Code Snippet

app.get(`${ROUTES.USERS}/:id`, async (request, response) => {
    const _id = request.params.id;
    try {
        // was getting error when not used await
        const user = await User.findById(_id);
        if (!user) {
            response.status(HTTP_STATUS_CODES.NOT_FOUND).send('no user found');
        } else {
            response.send(user);
        }
    } catch (e) {
        response
            .status(HTTP_STATUS_CODES.INTERNAL_SERVER_ERROR)
            .send('Something went wrong, try again after some time.');
    }
});

This is because JavaScript structures that include circular references can't be serialized with a"plain" JSON.stringify.

https://www.npmjs.com/package/circular-json mentioned by @Dinesh is a good solution. But this npm package has been deprecated.

So use https://www.npmjs.com/package/flatted npm package directly from the creator of CircularJSON.

Simple usage. In your case, code as follows

import package

// ESM
import {parse, stringify} from 'flatted';

// CJS
const {parse, stringify} = require('flatted');

and

console.log("Request data " + stringify(req));

Came across this issue in my Node Api call when I missed to use await keyword in a async method in front of call returning Promise. I solved it by adding await keyword.

          AxiosService({
            method: 'POST',
            url: '/products',
            data: {
                name: productNumber,
                number: productNumber,
                description: productDescription,
                type: category,
                price: 0,
            },
        })

In my case I made mistake in the payload data when making request. By mistake I was setting description as e.target instead of e.target.value when taking input.

I came across this issue when not using async/await on a asynchronous function (api call). Hence adding them / using the promise handlers properly cleared the error.

I was missing .toArray() when making a call to a MongoDB collection to retrieve multiple documents.

This was throwing the error: doc = await database.find({ "type": ctx.params.type });

This was the fix: doc = await database.find({ "type": ctx.params.type }).toArray();

Here's a link to the documentation about it: https://www.mongodb.com/docs/manual/reference/method/cursor.toArray/

One of the reasons I got this error was that I was sending the full response object returned by Axios using res.send() in an Express app.

app.get('/fetch', async (req, res) => {
  const targetUrl = req.query.url;

  if (!targetUrl) {
    return res.status(400).json({ error: 'Missing url query parameter' });
  }

  try {
    const response = await axios.get(targetUrl, {
      headers: {
        'Accept': 'text/html',
      }
    });
    
    await res.status(200).send(response);
  } catch (error) {
    console.error('Error fetching:', error.message);
    res.status(500).json({ error: 'Failed to fetch content' });
  }
});

These objects often contain non-serializable internal fields — especially in the case of Axios. For example, response.request and response.config can contain circular references like:

request → response → request

I solved it by sending only the data field as the response, but I'm still looking for a solution that would allow me to send the entire response object safely.

If an object has a different type of property like mentioned in the above image, JSON.stringify() will through an error.

For mongodb

so if you are getting errors while fetching data from MongoDB then the problem is async

previously

app.get('/users',(req,res,next)=>{
 
 const user=chatUser.find({});
 
 if(!user){
 
 res.status(404).send({message:"there are no users"});
 
 
 }
 
 if(user){
 
 res.json(user);
 
 }
})

After

app.get('/users',async(req,res,next)=>{
 
 const user=await chatUser.find({});
 
 if(!user){
 
 res.status(404).send({message:"there are no users"});
 
 
 }
 
 if(user){
 
 res.json(user);
 
 }
 
})

Edit May 22, 2023

I think it is an error which need to be fixed not a feature which is needed. I have faced this issue and tried following things. Hope it helps.

1. The reference does not have resolved value till the time, we are going to use it. In this case, I have awaited the response, by adding await keyword and checking whether I am returning proper value from the function.

2. In the second case when I faced this issue I had a json like,

   { obj1: "sample1", obj2: "sample2", obj3: obj3 }

or,

{
 obj1: "sample1",
 obj2: obj1
}

in this case, the value of any of the key in object is again depended on some other key, which was growing the json object recursively. Here, I fixed this dependency of one key on another to resolve it.