Designing Robust Applications with SOLID Principles

What are SOLID Principles?

SOLID is an acronym that represents five object-oriented design (OOD) guidelines designed to help developers create robust applications. These principles are:

• Single-responsibility principle
• Open–closed principle
• Liskov substitution principle
• Interface segregation principle
• Dependency inversion principle

The Single Responsibility Principle

The single responsibility principle (SRP) states that functions and classes should have only one job. This principle is essential in JavaScript, as it helps avoid coupling responsibilities, making applications more fragile and prone to errors.

A Real-World Example

Consider a Car model that not only represents a car but also fetches cars from an endpoint. This violates the SRP, as the Car class has two responsibilities. To fix this, we can separate the responsibilities into different classes:

class Car {
  // manage a car
}

class CarService {
  // handle getting and saving cars from an endpoint
}

Applying SRP in React

In React, a component that subscribes to a store, fetches data, renders a list, and ties to business logic is not reusable. To fix this, we can separate concerns by creating a MoviesList component that expects a movies array from its props. This way, the Movies component only deals with subscribing to the store, getting data, and passing it to the MoviesList component.

function Movies() {
  const movies = // fetch data from store
  return <MoviesList movies={movies} />;
}

function MoviesList({ movies }) {
  // render the list of movies
}

Applying SRP in Angular

In Angular, components are composed of smaller units of view. A component should have a single responsibility, such as displaying a feed or handling user input. We can break down an application into separate components, each with its own responsibility, making it easier to maintain and optimize.

@Component({
  selector: 'app-feed',
  template: '<div>{{ feed }}</div>'
})
class FeedComponent {
  feed = // fetch data from endpoint
}

@Component({
  selector: 'app-input',
  template: '<input>'
})
class InputComponent {
  // handle user input
}

Side Effects and Performance

Side effects can occur when the app state changes, leading to performance issues. In React, side effects can be handled using the useEffect hook, which prevents stale data.

import { useState, useEffect } from 'eact';

function Movies() {
  const [movies, setMovies] = useState([]);

  useEffect(() => {
    // fetch data from store
    setMovies(data);
  }, []);

  return <MoviesList movies={movies} />;
}

In Angular, smart components can cause side effects, making them hard to optimize. To mitigate this, we can use effects and move data to a store, making our components more predictable and optimizable.

Container and Presentational Components

Container components are self-contained and can generate and render their own data. Presentational components get their data from their parent and are “dumb” in that they can’t generate their own data. Understanding the difference between these components is crucial in designing reusable and maintainable applications.

By applying the single responsibility principle and other SOLID principles, we can create robust, scalable, and maintainable applications that are easier to debug and optimize. Remember, it’s not just about writing code, but about writing code that’s easy to understand and maintain.