Service layer pattern in Express - Mini Project: Build & Apply

Building a Service Layer in Express

📖 Scenario: You are creating a simple Express app to manage a list of books. To keep your code clean and organized, you will use the Service Layer pattern. This means you will separate the logic that handles data from the code that handles HTTP requests.

🎯 Goal: Build an Express app with a service layer that manages book data. You will create the data, add a configuration variable, write the service logic to get books, and finally connect the service to an Express route.

📋 What You'll Learn

Create an array called books with three book objects, each having id, title, and author properties

Add a variable called maxBooks set to 3 to limit how many books the service returns

Create a service function called getBooks that returns books up to maxBooks

Set up an Express route /books that uses the getBooks service to send JSON response

💡 Why This Matters

🌍 Real World

Many web apps separate business logic from routing to keep code clean and reusable. Service layers help organize code for features like user management, product catalogs, or orders.

💼 Career

Understanding service layers is important for backend developers working with Express or similar frameworks. It shows good coding practices and prepares you for larger projects.

1

Create the initial book data

Create an array called books with these exact three objects: { id: 1, title: 'The Hobbit', author: 'J.R.R. Tolkien' }, { id: 2, title: '1984', author: 'George Orwell' }, and { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee' }.

Express

// Create the books array with 3 book objects
// Your code here

Need a hint?

Use const books = [ ... ] and include exactly three objects with the given properties.

2

Add a configuration variable

Add a variable called maxBooks and set it to 3. This will limit how many books the service returns.

Express

const books = [
  { id: 1, title: 'The Hobbit', author: 'J.R.R. Tolkien' },
  { id: 2, title: '1984', author: 'George Orwell' },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee' }
];

// Add maxBooks variable below
// Your code here

Need a hint?

Use const maxBooks = 3; to create the variable.

3

Create the service function

Write a function called getBooks that returns the first maxBooks items from the books array using the slice method.

Express

const books = [
  { id: 1, title: 'The Hobbit', author: 'J.R.R. Tolkien' },
  { id: 2, title: '1984', author: 'George Orwell' },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee' }
];

const maxBooks = 3;

// Write getBooks function below
// Your code here

Need a hint?

Define function getBooks() and return books.slice(0, maxBooks).

4

Connect service to Express route

Set up an Express app. Import express, create app with express(), and add a GET route /books that sends JSON response using the getBooks function. Finally, listen on port 3000.

Express

const books = [
  { id: 1, title: 'The Hobbit', author: 'J.R.R. Tolkien' },
  { id: 2, title: '1984', author: 'George Orwell' },
  { id: 3, title: 'To Kill a Mockingbird', author: 'Harper Lee' }
];

const maxBooks = 3;

function getBooks() {
  return books.slice(0, maxBooks);
}

// Import express, create app, add /books route using getBooks, and listen on port 3000
// Your code here

Need a hint?

Use require('express'), create app, add app.get('/books', ...) route, and call app.listen(3000).