Library API (TypeScript + Express)

A minimal RESTful API to manage Authors and Books using in-memory storage, built with TypeScript and Express.

Features

• Full CRUD operations for Authors and Books
• One-to-many relationship: each Book references an existing Author via authorId
• Input validation middleware for POST and PUT requests
• Duplicate detection (case-insensitive) for both authors and books
• Cascade delete: removing an author also removes all their books
• Filtering, sorting & pagination on the books listing endpoint
• Request logging middleware (timestamp + method + URL)
• Centralized error handling with a custom AppError class
• Comprehensive TypeScript types — explicit interfaces for all entities, request payloads, and API responses

Project Structure

src/
├── index.ts               # Express app setup and server startup
├── types/
│   └── index.ts           # Centralized TypeScript interfaces and types
├── models/
│   ├── author.ts          # Author entity, in-memory store, ID generator
│   └── book.ts            # Book entity, in-memory store, ID generator
├── middleware/
│   ├── logger.ts          # Request logging middleware
│   ├── errorHandler.ts    # Global error-handling middleware
│   └── validation.ts      # Body validation for authors and books
├── routes/
│   ├── authors.ts         # CRUD + nested routes for /authors
│   └── books.ts           # CRUD + query routes for /books
└── utils/
    └── errors.ts          # Custom AppError class

Quick Start

Prerequisites

• Node.js v16+ and npm v8+

Installation

npm install

Development (hot-reload)

npm run dev

The API will be available at http://localhost:3000.

Production

npm run build
npm start

Environment Variables

Copy .env.example to .env and adjust as needed:

Variable	Default	Description
PORT	3000	Port the server listens on

API Endpoints

Authors

Method	Endpoint	Description
POST	/authors	Create a new author { name, bio? }
GET	/authors	List all authors
GET	/authors/:id	Get a single author by ID
PUT	/authors/:id	Update an author { name, bio? }
DELETE	/authors/:id	Delete an author (cascades to books)
GET	/authors/:id/books	List all books by an author

Books

Method	Endpoint	Description
POST	/books	Create a new book { title, year?, authorId }
GET	/books	List books (with optional filters — see below)
GET	/books/:id	Get a single book by ID
PUT	/books/:id	Update a book { title, year?, authorId }
DELETE	/books/:id	Delete a book

Book Query Parameters

Parameter	Type	Description
title	string	Filter by title (case-insensitive substring match)
author	string	Filter by author name (case-insensitive substring)
year	number	Filter by exact publication year
sort	string	Sort by field + direction (e.g. year_desc, title_asc)
limit	number	Max results per page
page	number	Page number (1-indexed, default 1)

Error Handling

All errors follow a consistent JSON format:

{
  "error": "Human-readable error description"
}

Status Code	Meaning
400	Validation failed
404	Resource not found
409	Duplicate / conflict
500	Internal server error

Design Decisions

• In-memory storage: Data lives in JavaScript arrays — simple, no database setup required, but data is lost on restart. Suitable for learning and assessment.
• Cascade deletion: Deleting an author removes all associated books to prevent orphaned references.
• Centralized types: All TypeScript interfaces are defined in src/types/index.ts for consistency and maintainability.
• Custom AppError class: Enables route handlers to throw structured errors with HTTP status codes, handled cleanly by the error middleware.

Scripts

Script	Command	Description
npm run dev	ts-node-dev --respawn ...	Start dev server with hot-reload
npm run build	tsc	Compile TypeScript to dist/
npm start	node dist/index.js	Run the compiled production build

Tech Stack

Technology	Version	Purpose
TypeScript	^5.2.2	Static type safety
Express	^4.18.2	HTTP framework
body-parser	^1.20.2	JSON request body parsing
cors	^2.8.5	Cross-Origin Resource Sharing
ts-node-dev	^2.0.0	Development server with hot-reload