Deep Copy & Shallow Copy in 10 Minutes | Javascript Interview Question 🚀 ( Interview Special )

Summary

In this video, the presenter explains the difference between Shallow Copy and Deep Copy in JavaScript, a crucial concept for developers. The tutorial demonstrates how Shallow Copy duplicates top-level properties while retaining references for nested objects, making changes to the original object reflect in the copy. In contrast, a Deep Copy creates an entirely new object with new references, ensuring that changes in the original do not affect the copy. The video includes practical examples and insights, making it easy to understand these concepts for use in real-world applications and interviews.

Takeaways

• 😀 Shallow copy and deep copy are crucial concepts in JavaScript, often discussed in interviews.
• 😀 A shallow copy only copies the top-level properties of an object; nested objects retain the same reference.
• 😀 The spread operator (`...`) and `Object.assign()` are two common methods to create a shallow copy.
• 😀 When you modify the original object’s nested properties, the shallow copy will reflect those changes because both share the same memory reference for nested objects.
• 😀 A deep copy, on the other hand, creates a completely independent copy, including for nested objects.
• 😀 To create a deep copy, you can use `JSON.stringify()` and `JSON.parse()` to ensure the object’s properties are deeply cloned.
• 😀 In the case of a shallow copy, changes to nested objects in the original will be visible in the shallow copy due to shared references.
• 😀 With a deep copy, even if you modify the original object’s nested properties, the deep copy remains unaffected.
• 😀 Understanding when to use shallow copy and deep copy depends on your use case, especially when dealing with nested objects.
• 😀 This distinction between shallow and deep copy is essential for understanding memory management and preventing unexpected bugs in your code.

Q & A

What is the main difference between shallow copy and deep copy in JavaScript?

The main difference is that a shallow copy creates a new object but does not clone nested objects. Instead, it references the original nested objects. A deep copy, on the other hand, creates a completely new object with its own independent references, including for nested objects.

How does JavaScript handle memory allocation when creating an object?

In JavaScript, when an object is created, memory is allocated for it. The variables and functions are stored in memory, and the object gets a memory reference. This reference is used to access and manipulate the object.

What happens when we make a shallow copy of an object using the spread operator?

When we use the spread operator to make a shallow copy, a new object is created with the same properties as the original object. However, if the object contains nested objects, the nested objects are not copied but instead referenced, meaning any changes to nested objects in the original will reflect in the shallow copy.

Can you explain the concept of 'memory reference' in the context of shallow copy?

Memory reference refers to the pointer or location in memory where an object or value is stored. In shallow copy, the reference to nested objects is shared between the original object and its copy, which means changes to nested objects in one will affect the other.

How do you create a shallow copy of an object using Object.assign()?

To create a shallow copy using Object.assign(), you pass an empty object as the first argument and the original object as the second. This creates a new object with the same properties as the original but with references to the same nested objects.

What will happen if we modify a property of a nested object in the original object after creating a shallow copy?

If you modify a nested object's property in the original object after creating a shallow copy, the change will be reflected in the shallow copy as well. This is because both the original object and the shallow copy share the same memory reference for the nested objects.

How can you create a deep copy of an object in JavaScript?

To create a deep copy, you can stringify the object (convert it into a JSON string) and then parse it back into a new object. This process creates new memory references for the original object and all of its nested objects, making the deep copy independent of the original.

Why does a deep copy not reflect changes made to the original object?

A deep copy does not reflect changes made to the original object because it creates a completely new object with separate memory references. The nested objects in the deep copy are also independently copied, so modifications to the original object will not affect the deep copy.

What is the impact of using a deep copy when dealing with complex objects with nested properties?

Using a deep copy for complex objects with nested properties ensures that both the top-level object and its nested properties are independently copied. Any changes to the original object or its nested properties will not affect the deep copy, making it suitable for situations where you need to maintain the original object unchanged.

How can you decide whether to use a shallow copy or a deep copy in your JavaScript code?

The decision to use a shallow or deep copy depends on the use case. If you need to preserve the references to nested objects and only modify top-level properties, a shallow copy is sufficient. If you need to modify the original object and keep the copy unaffected, especially for nested properties, a deep copy is the better choice.