Converting circular structure to JSON

Broken code example

const user = {};
user.self = user;
JSON.stringify(user);

Corrected example

const user = {};
JSON.stringify(user);

Why this error happens

JSON does not have a native way to represent an object that points back to itself. When JSON.stringify discovers that cycle, it throws instead of producing invalid or misleading output.

How to fix it

1. Remove the circular reference if it is not needed.
2. Create a plain serializable copy of the object.
3. Use a custom replacer when you intentionally want to skip circular branches.
4. Then validate or format the resulting JSON string if needed.