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Discussion on: Shallow Copy vs Deep Copy in JavaScript

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jonrandy profile image
Jon Randy 🎖️ • • Edited

The easiest way to achieve this in JavaScript is by using JSON.parse(JSON.stringify(object))

Not really. Using the built in structuredClone is even easier, and works better:

const copy = structuredClone(object)
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rajusaha profile image
Raju Saha •

@jonrandy
Thanks 😊

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sudhirkumar1003 profile image
Sudhir Kumar • • Edited

Thanks you. Wasn't aware about this fn.

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jahid6597 profile image
MD. JAHID HOSSAIN •

JSON.parse(JSON.stringify(object)) efficiently creates a copy of simple objects by converting them to a JSON string and back, but loses complex data types like NaN, Set and Map. structuredClone preserves complex data types and handles NaN and Set, but doesn't support functions or symbols and may not be universally available.

Let's take an example:

const original = {
  value: undefined,
  infinity: Infinity,
  nan: NaN,
  date: new Date(),
  regExp: /hello/i,
  buffer: new ArrayBuffer(10),
  nested: {
    set: new Set([1, 2, 3]),
    map: new Map([["key1", "value1"], ["key2", "value2"]])
  },
  //   func: function() { return "Hello"; },
  //   symbol: Symbol('sym')
};
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original object containing various data such as undefined, Infinity, NaN, Date, RegExp, ArrayBuffer, Set and Map. Properties func and symbol are commented.

const clonedJSON = JSON.parse(JSON.stringify(original));
console.log(clonedJSON);
// {
//   "infinity": null,
//   "nan": null,
//   "date": "2024-06-24T07:08:01.362Z",
//   "regExp": {},
//   "buffer": {},
//   "nested": {
//     "set": {},
//     "map": {}
//   }
// }
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JSON.parse(JSON.stringify(object))

  • Loses undefined, Infinity, NaN, functions, symbols, RegExp, Date, Set, Map, ArrayBuffer, and other non-JSON data types.
  • Suitable for simple, plain objects without complex data types or structures. 
const clonedStructured = structuredClone(original);
console.log(clonedStructured);
// {
//   "value": undefined,
//   "infinity": null,
//   "nan": null,
//   "date": "2024-06-24T07:08:01.362Z",
//   "regExp": {},
//   "buffer": {},
//   "nested": {
//     "set": {},
//     "map": {}
//   }
// }
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structuredClone

  • Preserves most data types including undefined, Infinity, NaN, RegExp, Date, Set, Map, ArrayBuffer.
  • Does not clone functions or symbols.
  • Suitable for complex objects and structures requiring accurate deep copying.

Case #1

console.log(clonedJSON.nan); // null
// `clonedJSON.nan` will be `null` because `NaN` cannot be represented in JSON and is lost during the stringify operation

console.log(clonedStructured.nan); // NaN
// `clonedStructured.nan` remains `NaN` because `structuredClone` is designed to handle complex JavaScript objects and can correctly preserve `NaN` during the cloning process.
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Case #2

console.log(clonedJSON.nested.set); // {}
// `clonedJSON.nested.set` will be `{}` because the `Set` is lost during the `stringify` operation.

console.log(clonedStructured.nested.set); // Set (3) {1, 2, 3}
// `clonedStructured.nested.set` remains a `Set` object containing the same values `[1, 2, 3]` as in the `original` object.
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rajusaha profile image
Raju Saha •

@jahid6597
Thanks 😊 As I am still learning and was not aware about the structuredClone