In JavaScript, a deep copy refers to creating a completely independent duplicate of a complex data structure, such as an object or an array, including all nested objects and arrays within it. Unlike a shallow copy, a deep copy ensures that changes made to the original data structure do not affect the copied one, and vice versa.

To achieve a deep copy, each level of the data structure must be recursively traversed, and new objects or arrays must be created to hold the copied values. This process ensures that every nested object or array is duplicated, rather than just copying references to them.

Example: Here, JSON.stringify() converts the original object to a JSON string, and JSON.parse() then parses that string back into a new object. This process creates a deep copy of the original object, including its nested properties. As a result, modifying the properties of the original object after copying does not affect the deep copy.

{
  name: 'Alice',
  age: 30,
  address: { city: 'Los Angeles', country: 'USA' }
}
{
  name: 'John',
  age: 30,
  address: { city: 'New York', country: 'USA' }
}