Introduction

In programming, the concepts of deep copy and shallow copy are not limited to a single language but are essential for data manipulation in various programming languages, including JavaScript. These concepts are fundamental to understanding how data is duplicated and managed in your code. In this blog, we will explore deep copy and shallow copy, their significance, and their relevance in different programming languages.

Understanding Copying

Before talking about deep and shallow copies, Let's understand what it means to copy data in programming. Copying data entails creating a new instance that replicates the contents of the original data, allowing you to work with it independently.

Shallow Copy

A shallow copy, in JavaScript and other languages, copies the outermost structure of an object or data structure but still references the same memory location as the original object. The method to create a shallow copy varies depending on the programming language. For example, in JavaScript, you can use the spread operator or Object.assign() to create a shallow copy.

Consider this JavaScript example:

let originalArray = [1, [2, 3], 4];
let shallowCopiedArray = [...originalArray];

shallowCopiedArray[1][0] = 5;

console.log(originalArray);         // Output: [1, [5, 3], 4]
console.log(shallowCopiedArray);  // Output: [1, [5, 3], 4]

In the above example we can see that when we modify the inner array within the shallow copy, the original array is also affected. Shallow copying copies references to inner objects, not the objects themselves.

It's useful when you want to create a new object that references the same memory location as the original. However, It's not suitable when you need to isolate the data completely.

Deep Copy

In contrast, a deep copy duplicates the entire structure of an object, including all nested objects and allocates a separate memory location for the new Object. This means that a deep copy creates a completely independent copy of the original data, allowing you to modify it without affecting the original.

Consider this JavaScript example:

const originalArray = [1, [2, 3], 4];
const deepCopiedArray = JSON.parse(JSON.stringify(originalArray));

deepCopiedArray[1][0] = 5;

console.log(originalArray);         // Output: [1, [2, 3], 4]
console.log(deepCopiedArray);       // Output: [1, [5, 3], 4]

in the above example JSON.stringify() to convert originalArray to a JSON string, and then use JSON.parse() to convert that string back to a new object deepCopiedArray. It creates a deep copy of originalArray & any modifications to the new array won't change the original array.

Conclusion

Understanding the difference between deep copy and shallow copy is vital for effective data manipulation in programming. Whether you are working with JavaScript or any other programming language, knowing when and how to use these techniques can make your code more robust and efficient. These concepts transcend the boundaries of languages and are fundamental for any programmer aiming to work with complex data structures and ensure data integrity.