Why JSON.parse(JSON.stringify) Fails for Deep Cloning and What to Use Instead

In JavaScript development, deep cloning objects is a common need. Many developers use the one‑line solution JSON.parse(JSON.stringify(obj)), but this approach has many unexpected problems. This article reveals its flaws and presents several more reliable deep‑clone alternatives.

Fatal Flaws of JSON.stringify

The JSON.parse(JSON.stringify(obj)) method looks simple and elegant, but it has serious limitations. Below are situations it cannot handle correctly:

1. Cannot handle circular references

const obj = { name: "对象" };
obj.self = obj; // circular reference
// Throws error: TypeError: Converting circular structure to JSON
const copy = JSON.parse(JSON.stringify(obj));

When an object contains a circular reference, this method throws an error and crashes the program.

2. Loss of special data types

JSON serialization cannot handle functions, Symbol, undefined; it converts Date to a string, RegExp to an empty object, and NaN/Infinity to null.

3. Prototype chain loss

After deep cloning, the object becomes a plain object, losing all methods and properties defined on its prototype chain.

4. Handling of Map, Set, WeakMap, WeakSet

These collection types are turned into empty objects during JSON serialization, resulting in complete data loss.

More Reliable Deep Clone Alternatives

Since the JSON method has many pitfalls, what are better alternatives? Modern browsers provide the native Structured Clone API structuredClone, which can handle most cases:

// One‑line deep clone
const copy = structuredClone(original);

Advantages:

Supports circular references

Supports most built‑in types (Date, RegExp, Map, Set, etc.)

Performance superior to the JSON method

Disadvantages:

Does not support functions, DOM nodes, or prototype chains

Although the one‑line JSON.parse(JSON.stringify(obj)) solution looks concise and elegant, it has too many defects and may introduce unexpected bugs in real projects. The native structuredClone API is the most recommended simple replacement for deep cloning in modern JavaScript.