How Can You Determine if Something Is a Deep Copy in JavaScript?

Shallow copies only duplicate the top-level structure of an object, while deep copies create new instances of all nested objects and their properties. By comparing the references of the nested objects (orig.nested === shallowCopy.nested and orig.nested === deepCopy.nested), we can determine whether a shallow or deep copy has been made.

const orig = {
  nested: {
    value: 1,
  },
};

const shallowCopy = { ...orig };
const deepCopy = {
  ...orig,
  nested: { ...orig.nested },
};

console.log(orig.nested === shallowCopy.nested); // true - not a deep copy
console.log(orig.nested === deepCopy.nested); // false - deep copy created