How to Set up Basic Node.js + Express.js Server with TypeScript

Getting Started

First things first, we need to create the directory for our application:

bash
mkdir express-typescript

Time to set up our package.json file where we can define all our dependencies as well as executable scripts.

bash
npm init

Once this script is run, it will ask us the following questions:

bash
package name: (src) express-typescript
version: (1.0.0)
description:
entry point: index.ts
test command:
git repository:
keywords:
author:
license: (ISC)

Feel free to provide the correct details. For now, the only information we cared to provide is the package name and the entry point set to index.ts.

Installing Dependencies

Since we are going to work with Express.js, we need to install Express.

bash
npm i --save-dev express

We need to install TypeScript as well as Express types as part of the dev dependencies to take advantage of TypeScript

bash
npm i --save-dev typescript @types/express

Create Minimal Server with Express.js and TypeScript

Let’s create what could be considered the most basic server using Express.js. Inside the src folder, create an index.ts file and copy the following code:

typescript
import express, { Request, Response } from 'express';
const app = express();
const port = 3000;
app.get('/', (req: Request, res: Response) => {
  res.send('Hello World!');
});
app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
});

As you notice, it will be a simple GET API endpoint returning a message.

Running TypeScript Files in Node.js: Understanding the Process

First, it is important for us to understand the process that happens to run TypeScript files in node.js. Previously, we created a simple server inside the index.ts. If we were working with plain JavaScript, a similar code could be written in a js file such as index.js. Normally, we will run a js file using the node command.

bash
node src/index.js

If we try to do something similar with index.ts file, the terminal will fail due to syntax errors as we are writing code in TypeScript.

bash
// it will fail
node src/index.ts

What we need to do is to compile our TypeScript code into JavaScript code, and we are going to do that using the tsc command which it is available after installing typescript dependency in the project.

bash
npx tsc src/index.ts

This will generate an index.js file. Now that we have our JavaScript file, we can use node to run our code.

bash
node src/index.js

Running TypeScript Files in Node.js: Quick Process

There is a package available called ts-node which allows executing our TypeScript file in node. Therefore, we are going to install ts-node as part of our development dependencies.

bash
npm i --save-dev ts-node

Once the package is installed, we can run our project with only one command.

bash
npx ts-node src/index.ts

The best thing is that we don’t see any index.js file generated anymore

Setting up TypeScript Configuration

The tsconfig.json file specifies the root files and the compiler options required to compile a TypeScript project. Without it, our TypeScript project would still feel as a JavaScript project because we are not enforcing the usage of types in our codebase. Therefore, we are going to create a tsconfig.json file in the root folder of our project. Once this is done, add the following configuration:

json
{
  "compilerOptions": {
      "module": "commonjs",
      "esModuleInterop": true,
      "allowSyntheticDefaultImports": true,
      "target": "es6",
      "noImplicitAny": true,
      "moduleResolution": "node",
      "sourceMap": true,
      "outDir": "dist",
      "baseUrl": ".",
      "paths": {
          "*": [
              "node_modules/*",
              "src/types/*"
          ]
      },
  },
  "include": [
      "src/**/*"
  ]
}

Setting Up Scripts in the package.json

Now that we understand how to run TypeScript files, we can set up a start script in the package.json for our application.

json
"scripts": {
    "start": "npx ts-node src/index.ts"
},

Once we save, we can open the terminal and run npm run start and we will notice our project is running.