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TypeError: cyclic object value

The JavaScript exception "cyclic object value" occurs when object references were found in JSON. {{jsxref("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​

What went wrong?​

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

Examples​

Circular references​

In a circular structure like the following

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

{{jsxref("JSON.stringify()")}} will fail

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 {{jsxref("JSON.stringify()")}}:

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​

  • {{jsxref("JSON.stringify()")}}
  • cycle.js on GitHub