Single Responsibility Principle in JavaScript: Separating Concerns for More Maintainable Code

The Single Responsibility Principle (SRP) is one of the fundamental principles of software design, which states that a class or module should have only one reason to change. In other words, it should have only one responsibility. Violating this principle can result in code that is difficult to understand, maintain, and extend. In this article, we’ll discuss the SRP and provide an example of how it can be violated and then fixed in JavaScript. SRP is one of the principles of SOLID Design Principles.

Violating the SRP

Let’s take a look at an example of a violation of the SRP:

class User {
  constructor(name, email, password) {
    this.name = name;
    this.email = email;
    this.password = password;
  }
  
  saveToDatabase() {
    // Code to save user data to the database
  }
  
  sendEmail(emailBody) {
    // Code to send email to the user
  }
}

In the example above, we have a User class that has two responsibilities. The first is to save the user’s data to the database, and the second is to send an email to the user. This is a clear violation of the SRP, as the User class is responsible for both data persistence and email functionality.

This code violates the SRP for a few reasons. First, it’s not easy to understand what the class is responsible for. Second, it’s difficult to modify and extend because changes to one responsibility may impact the other. Lastly, this class can become bloated and unmaintainable over time as additional responsibilities are added.

Applying the SRP

To fix this violation of the SRP, we need to separate the responsibilities of the User class. One way to do this is to create separate classes for each responsibility. Let’s see how this can be done:

class User {
  constructor(name, email, password) {
    this.name = name;
    this.email = email;
    this.password = password;
  }
}

class UserRepository {
  saveUser(user) {
    // Code to save user data to the database
  }
}

class EmailService {
  sendEmail(email, emailBody) {
    // Code to send email to the user
  }
}

In this example, we have created three classes: User, UserRepository, and EmailService. The User class is responsible for holding user data. The UserRepository class is responsible for saving the user data to the database. The EmailService class is responsible for sending emails.

By separating the responsibilities into different classes, we have made the code more maintainable and easier to understand. Each class has a single responsibility, making it easier to modify and extend the code over time. Additionally, if there is a bug in the email functionality, it won’t impact the database functionality, and vice versa.

Conclusion

The Single Responsibility Principle is a critical principle in software design. By following this principle, we can create code that is easier to understand, maintain, and extend. Violating this principle can lead to code that is difficult to work with and can cause problems down the road. By separating responsibilities into separate classes, we can create more modular and flexible code that is easier to manage.