In this article, we will learn what shallow copy is and how to use it in any project. We'll break down everything about what shallow copy means and give you all the details you need to work with your data like a pro.
Let's dive in!
Table of contents
- What is a shallow copy?
- When should we use shallow copying?
- In how many ways can we use shallow copy?
- Which is the best method for implementing shallow copying?
- Practical Pointers
1. What is a shallow copy?
A shallow copy, sometimes called a bit-wise copy, makes a duplicate of an object's structure but keeps the same values. It's like making a copy of a picture without changing anything in it.
Shallow copying in JavaScript duplicates the structure and basic properties of an object but maintains shared references to nested objects. It's like making a copy of a box with smaller boxes inside. The copied box has the same contents as the original, but changes to the contents of the smaller boxes in the copy affect the original. JavaScript provides methods like Object.assign() or spread syntax (...) for effortless shallow copying.
For example, we have an object representing a person named Elena, who is 21 years old and has contact details like an email and phone number. Now, let's create a copy of this person object using the spread operator (...) for shallow copying. This means we're making a new object with the same name and age properties as Elena. However, the crucial point to note is that the contact object, which holds Elena's email and phone, is still referenced rather than copied. So, when we modify the email in the copied object to 'something@gmail.com', it directly alters the original person object's email as well. Both the original and copied objects share the same contact object, leading to this direct impact.
I'll share a code example to help you grasp the idea of shallow copying and what it means in JavaScript.
// Original object representing a person
const originalPerson = {
name: "Elena",
age: 21,
contact: {
email: "Elena@example.com",
phone: "123-456-7890"
}
};
// Shallow copy using spread operator (...)
const shallowCopyPerson = { ...originalPerson };
// Modifying the contact object in the shallow copy
shallowCopyPerson.contact.email = "something@gmail.com";
// Outputting both the original and copied objects
console.log("Original Person:", originalPerson);
console.log("Shallow Copy Person:", shallowCopyPerson);Output:
// Original Person: { name: 'Elena', age: 21, contact: { email: 'something@gmail.com', phone: '123-456-7890' } }
// Shallow Copy Person: { name: 'Elena', age: 21, contact: { email: 'something@gmail.com', phone: '123-456-7890' } }When we created shallowCopyPerson as a reference to originalPerson in JavaScript using the spread operator (...), they both shared the same memory address. This means any changes made to one object will affect the other since they're essentially pointing to the same location in memory. In the above code snippet, modifying the email address of the contact object in shallowCopyPerson directly impacts the originalPerson object as well.
2. When should we use shallow copying?
Shallow copying comes in handy when you want to make a quick copy of an object's basic structure and simple properties without getting into all the details of its nested parts. It's great for situations where you just need a simple duplicate and don't need separate copies of everything inside.
However, be careful because changes to nested objects in the shallow copy will affect the original. Use shallow copying when you need a lightweight clone for simple data structures or when performance is a priority.
3. In how many ways can we use shallow copy?
In JavaScript, there are many ways to perform shallow copying, but I'll focus on two of the most common.
#1. Spread Operator:
The spread operator (...) can be used to create shallow copies of objects and arrays.
const original = {
name: "Elena",
age: 21
};
const shallowCopy = { ...original };
shallowCopy.name = "John"
console.log(original); // { name: 'Elena', age: 21 }
console.log(shallowCopy); // { name: 'John', age: 21 }#2. Object.assign():
The Object.assign() method can be used to copy the values of all countable properties from one or more source objects to a target object. This method can also be utilized for shallow copying.
const original = {
name: "Elena",
age: 21
};
const shallowCopy = Object.assign({}, original);
shallowCopy.name = "John"
console.log(original); // { name: 'Elena', age: 21 }
console.log(shallowCopy); // { name: 'John', age: 21 }4. Which is the best method for implementing shallow copying?
The spread operator (...) is a popular tool in JavaScript for making shallow copies. It's appreciated for its simplicity, clarity, and concise syntax. With just a single line of code, developers can easily make copies of objects and arrays without much hassle.
In addition, the spread operator is widely supported in modern JavaScript environments, making it a practical option for various scenarios. Overall, the spread operator (...) is the preferred method for shallow copying due to its ease of implementation and usability.
5. Practical Pointers
When copying objects and arrays in JavaScript, a shallow copy is often handy, but it's not always the best choice. Avoid shallow copies when you need deep copies or want to prevent unintended side effects from modifying nested object structures.
In such cases, consider using deep copy techniques like custom recursive function or JSON serialization, or embrace immutability principles to avoid copying altogether.
Shallow copy is useful when you want to quickly duplicate an object or array in JavaScript, especially for simple data structures.
You should avoid shallow copy like this scenario:
- If you need to duplicate nested objects or arrays recursively (deep copy).
- Modifying the copied object's nested structures should not affect the original.
- Preventing unintended side effects from shared references between original and copied objects.
Instead of shallow copy, consider deep copy:
- Deep copy techniques like recursive or JSON serialization allow complete duplication of nested structures.
- Embracing immutability principles to avoid the need for copying altogether, ensuring data integrity, and preventing unintended modifications.
Conclusion
Shallow copying is efficient for duplicating simple data structures, but it's important to consider its limitations, and it's more useful in scenarios where we don't need to modify nested objects independently.
Alternatives such as deep copy techniques or immutability may be preferable. Remember to consider the implications of sharing references between original and copied objects to avoid unintended side effects.
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