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snippets/js/s/stringify-circular-json.md

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+---
+title: Stringify circular JSON
+type: snippet
+language: javascript
+tags: [object]
+cover: periscope
+dateModified: 2020-10-22T20:24:30+03:00
+---
+
+Serializes a JSON object containing circular references into a JSON format.
+
+- Create a `WeakSet` to store and check seen values, using `WeakSet.prototype.add()` and `WeakSet.prototype.has()`.
+- Use `JSON.stringify()` with a custom replacer function that omits values already in `seen`, adding new values as necessary.
+- ⚠️ **NOTICE:** This function finds and removes circular references, which causes circular data loss in the serialized JSON.
+
+```js
+const stringifyCircularJSON = obj => {
+  const seen = new WeakSet();
+  return JSON.stringify(obj, (k, v) => {
+    if (v !== null && typeof v === 'object') {
+      if (seen.has(v)) return;
+      seen.add(v);
+    }
+    return v;
+  });
+};
+```
+
+```js
+const obj = { n: 42 };
+obj.obj = obj;
+stringifyCircularJSON(obj); // '{"n": 42}'
+```