replacer function for json.stringify to change circular references

json-stringify-circular-replacer.js

function circularReferenceReplacer () {
	const seen = new WeakMap();
	return (key, value) => {
		if (typeof value === "object" && value !== null) {
			if (seen.has(value)) {
				let path = seen.get(value);
				if (path === "") {
					path = "the root object";
				}
				return 'circular reference which points to ' + path + '.';
			}
			seen.set(value, key);
		}
		return value;
	};
}