How to Write a REST API in TypeScript in 30 Minutes: For Beginners

Introduction

Modern web development is unthinkable without a REST API. It is the foundation on which mobile applications, SPA frontends, and microservices are built. If you are a beginner and want to quickly learn backend development, the TypeScript + Express stack is an ideal start. TypeScript adds strict typing to JavaScript, making the code more reliable and understandable, especially when working in a team.

In this guide, we will create a full-fledged REST API for managing a task list (Todo list) in 30 minutes. You will learn how to set up a project, describe data models, create routes, and connect a database. No unnecessary theory — just practice and ready-to-run code.

It is assumed that you already have Node.js (version 18+) and npm installed. If not, download them from the official website.

1. Project Setup and Dependency Installation

Let's start by initializing a new TypeScript project. Open the terminal and run the commands:

mkdir my-todo-apicd my-todo-apinpm init -y

Now install the necessary packages:

npm install expressnpm install -D typescript @types/node @types/express ts-node nodemon

Create the TypeScript configuration file:

npx tsc --init

In the tsconfig.json file, make sure the following lines are uncommented and configured:

{  "compilerOptions": {    "target": "ES2020",    "module": "commonjs",    "outDir": "./dist",    "rootDir": "./src",    "strict": true,    "esModuleInterop": true,    "skipLibCheck": true,    "forceConsistentCasingInFileNames": true  },  "include": ["src/**/*"],  "exclude": ["node_modules", "dist"]}

Create the src folder and the src/index.ts file — this will be the entry point of our application.

Add scripts to package.json for convenient launch:

"scripts": {  "dev": "nodemon --exec ts-node src/index.ts",  "build": "tsc",  "start": "node dist/index.js"}

2. Creating a Basic Express Server

Now let's write a minimal Express server that will listen on port 3000. Open src/index.ts and add the following code:

import express, { Request, Response } from 'express';

const app = express();const PORT = 3000;

// Middleware for parsing JSONapp.use(express.json());

// Basic route for testingapp.get('/', (req: Request, res: Response) => {  res.send('Todo API is working!');});

app.listen(PORT, () => {  console.log(`Server running at http://localhost:${PORT}`);});

Start the server with the command npm run dev and open the browser at http://localhost:3000. You should see the message "Todo API is working!".

3. Defining the Data Model and In-Memory Storage

For simplicity, we will not connect a database right away, but will use temporary storage in RAM. Create the file src/models/todo.ts:

export interface Todo {  id: number;  title: string;  completed: boolean;  createdAt: Date;}

export let todos: Todo[] = [  { id: 1, title: 'Learn TypeScript', completed: false, createdAt: new Date() },  { id: 2, title: 'Write a REST API', completed: false, createdAt: new Date() },];

Notice the use of the Todo interface — this ensures that all objects in the array have the same structure.

4. Implementing CRUD Routes

Let's create the file src/routes/todos.ts with full routes for Create, Read, Update, and Delete operations.

import { Router, Request, Response } from 'express';import { Todo, todos } from '../models/todo';

const router = Router();

// GET /api/todos — get all tasksrouter.get('/', (req: Request, res: Response) => {  res.