The Right way to write Nest.js & Typescript clean-code - SOLID

Summary

This video script covers the five SOLID principles essential for TypeScript and NestJS developers to write cleaner, maintainable, and scalable code. It explains each principle with practical examples, starting with Single Responsibility, followed by Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion. The script guides viewers on applying these principles to elevate their coding skills from junior to senior level, using NestJS, a framework that integrates TypeScript for robust application development.

Takeaways

• 📝 The video discusses the importance of adhering to five SOLID principles for writing cleaner, more maintainable code in TypeScript and JavaScript.
• 🔑 The Single Responsibility Principle emphasizes that a class or module should have only one reason to change, focusing on a single task or functionality.
• 🔄 Open/Closed Principle encourages designing code to be open for extension but closed for modification, facilitated by dependency injection in frameworks like NestJS.
• 🔄 Liskov Substitution Principle states that derived classes should be substitutable for their base classes without affecting the program's correctness.
• 🔗 Interface Segregation Principle advises creating small, specific interfaces rather than large ones with unnecessary methods to avoid unused functionality.
• 🔄 Dependency Inversion Principle recommends depending on abstractions, not concrete implementations, to reduce coupling and ease testing and maintenance.
• 🛠️ The video provides practical examples of how to apply these principles in a NestJS framework, which uses TypeScript for features like interfaces, classes, and abstract classes.
• 📚 Understanding and applying SOLID principles can help developers transition from a junior to a senior level by writing more efficient and reusable code.
• 🔄 The script illustrates the Open/Closed Principle with a payment service example, showing how to avoid modifying existing code when adding new payment methods.
• 📧 An example of violating the Single Responsibility Principle is given, where an order service also handles email sending, instead of focusing solely on order processing.
• 📚 The Interface Segregation Principle is demonstrated by separating email, SMS, and push notification interfaces to avoid bloated interfaces with irrelevant properties.
• 🔄 The Dependency Inversion Principle is exemplified by abstracting storage services to allow for easy swapping between different storage solutions like S3 or Google Cloud without changing the service code.

Q & A

What are the five SOLID principles discussed in the video?

The five SOLID principles discussed in the video are Single Responsibility Principle, Open/Closed Principle, Liskov Substitution Principle, Interface Segregation Principle, and Dependency Inversion Principle.

What does the Single Responsibility Principle aim to achieve in code?

The Single Responsibility Principle aims to ensure that each class or module in an application is responsible for a single task or functionality, thereby making the code cleaner and easier to maintain.

Why is it important to separate the order submission process from the email sending process in the example given?

It is important to separate these processes because it adheres to the Single Responsibility Principle, making the order service only responsible for order-related tasks and not for sending emails, which improves code readability and maintainability.

What does the Open/Closed Principle suggest regarding the design of code?

The Open/Closed Principle suggests that code should be designed to be open for extension but closed for modification, meaning new functionality can be added without altering existing code.

How does the use of dependency injection in NestJS facilitate the Open/Closed Principle?

Dependency injection in NestJS facilitates the Open/Closed Principle by enforcing the use of abstractions, making it easier to extend the application with new functionality without modifying the existing codebase.

Can you explain the Liskov Substitution Principle with an example from the video?

The Liskov Substitution Principle states that derived classes should be substitutable for their base classes without affecting the correctness of the program. In the video, different pricing strategies (like regular and sale pricing) implement an abstract PricingService class, allowing for interchangeable pricing strategies without modifying the base class.

What is the Interface Segregation Principle and why is it important?

The Interface Segregation Principle is about defining fine-grained interfaces tailored to the specific needs of the consumers, avoiding the creation of large interfaces with unnecessary methods. It is important because it allows for better code reusability and maintainability.

How should interfaces be defined according to the Interface Segregation Principle?

Interfaces should be defined in a way that they are small and focused on a single responsibility, providing only the necessary properties and methods needed for a specific task.

What is the Dependency Inversion Principle and how does it differ from the other SOLID principles?

The Dependency Inversion Principle is about depending on abstractions rather than concrete implementations, which allows for loose coupling between components and easier testing and maintenance. It differs from other principles by focusing on the relationship between high-level and low-level modules, promoting the use of abstractions to reduce dependencies on specific implementations.

How does the video demonstrate the Dependency Inversion Principle in the context of file storage?

The video demonstrates the Dependency Inversion Principle by showing how to abstract the file storage service into an abstract class, allowing for different concrete implementations like S3 or Google Cloud Storage. This abstraction allows the controller to use the storage service without being tied to a specific storage implementation.

Why is it recommended to use abstract classes and interfaces in TypeScript when applying SOLID principles?

Using abstract classes and interfaces in TypeScript helps to define clear contracts for how classes should behave, promoting code reusability, maintainability, and adherence to the SOLID principles by enforcing a structure that separates concerns and allows for easier extension and modification.