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TypeError: cyclic object value

The JavaScript exception "cyclic object value" occurs when object references were found in JSON. JSON.stringify() doesn't try to solve them and fails accordingly.

Message

TypeError: Converting circular structure to JSON (V8-based)
TypeError: cyclic object value (Firefox)
TypeError: JSON.stringify cannot serialize cyclic structures. (Safari)

Error type

TypeError

What went wrong?

The JSON format per se doesn't support object references (although an IETF draft exists), hence JSON.stringify() doesn't try to solve them and fails accordingly.

Examples

Circular references

In a circular structure like the following

js
const circularReference = { otherData: 123 };
circularReference.myself = circularReference;

JSON.stringify() will fail

js
JSON.stringify(circularReference);
// TypeError: cyclic object value

To serialize circular references you can use a library that supports them (e.g. cycle.js) or implement a solution by yourself, which will require finding and replacing (or removing) the cyclic references by serializable values.

The snippet below illustrates how to find and filter (thus causing data loss) a cyclic reference by using the replacer parameter of JSON.stringify():

js
function getCircularReplacer() {
  const ancestors = [];
  return function (key, value) {
    if (typeof value !== "object" || value === null) {
      return value;
    }
    // `this` is the object that value is contained in,
    // i.e., its direct parent.
    while (ancestors.length > 0 && ancestors.at(-1) !== this) {
      ancestors.pop();
    }
    if (ancestors.includes(value)) {
      return "[Circular]";
    }
    ancestors.push(value);
    return value;
  };
}

JSON.stringify(circularReference, getCircularReplacer());
// {"otherData":123,"myself":"[Circular]"}

const o = {};
const notCircularReference = [o, o];
JSON.stringify(notCircularReference, getCircularReplacer());
// [{},{}]

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value