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
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
const circularReference = { otherData: 123 };
circularReference.myself = circularReference;
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
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
- JSON.stringify
- cycle.js on GitHub