Create an ExpressJS Application

This quick start will help you create an Express.js application using projen's TypeScript project. The NodeJS project is a little feature-light, so to show off more of projen's features, we'll use the TypeScript project instead.

To begin, make sure you have the version of NodeJS you want to use set up in your terminal. Running which node in bash/zsh/other POSIX shells, or Get-Command node in Powershell, should print the path to the NodeJS version you want to use. nvm is a popular tool for managing multiple versions of Node on a single machine. To select a version, run nvm use <version>.

To create a new TypeScript project, use npx projen new typescript:

npx projen new typescript --name=express-project

projen does not officially maintain a project for Express.js, so we need to install the dependencies and write some boilerplate code.

Dependencies

To add libraries, open .projenrc.js and add them to the deps array. For example, to add the express library, add the following line to .projenrc.ts:

import { typescript } from "projen";

const project = new TypeScriptProject({
  name: "express-project",
  // ...
  deps: ["express"],
  // ...
});

Then re-run npx projen to install the library.

Code

The most basic "Hello World!" example for Express.js consists of a single file, so let's create that file and the basic app now under src/index.ts (replace the contents of the file that's already there):

import express, { Request, Response } from "express";
const app = express();
const port = process.env.PORT || 3000;

app.get("/", (req: Request, res: Response) => {
  console.info(req);
  res.send("Hello World!");
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

Running the app

You have code now, but you need to run it! To do that, we'll add a start task to projen:

project.tasks.addTask("start", {
  exec: "ts-node src/index.ts",
  receiveArgs: true,
});

This will run the ts-node src/index.ts command when you run npx projen start. It also makes it possible to run npm start, pnpm start or yarn start, since projen updates package.json. The receiveArgs parameter allows you to pass additional arguments to the command.

Testing

Testing will require a few more dependencies, so let's add those now:

project.deps.addDevDeps("supertest", "@types/supertest");

Jest is added by default to a projen TypeScript project, so you don't need to specify it.

Next, let's update our code to make it testable:

src/index.ts

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

export const exampleApp = express(); // Export the app so we can test it
const port = process.env.PORT || 3000;

exampleApp.get("/", (req: Request, res: Response) => {
  console.info(req);
  res.send("Hello World!");
});

if (require.main === module) {
  // Check if the file is being run directly
  exampleApp.listen(port, () => {
    console.log(`Example app listening on port ${port}`);
  });
}

Now, let's create a test file under tests/index.test.ts (you can delete the default test file that's already there):

import request from "supertest";
import { exampleApp } from "../src/index";

describe("GET /", () => {
  it("responds with Hello World!", async () => {
    const response = await request(exampleApp).get("/");
    expect(response.status).toBe(200);
    expect(response.text).toBe("Hello World!");
  });
});

projen's TypeScript project comes with a test task already, so we just need to run npx projen test.

 PASS  test/index.test.ts
  GET /
    ✓ responds with Hello World! (23 ms)

----------|---------|----------|---------|---------|-------------------
| File       | % Stmts   | % Branch   | % Funcs   | % Lines   | Uncovered Line #s   |
| ---------- | --------- | ---------- | --------- | --------- | ------------------- |
| All files  | 77.77     | 66.66      | 50        | 77.77     |
| index.ts   | 77.77     | 66.66      | 50        | 77.77     | 12-13               |
| ---------- | --------- | ---------- | --------- | --------- | ------------------- |
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.164 s
Ran all test suites.
👾 test » eslint | eslint --ext .ts,.tsx --fix --no-error-on-unmatched-pattern src test build-tools projenrc .projenrc.ts

Extending the project

While Express.js can be run from a single file, it usually is not a best practice to do so. Instead, consider following the structure created by the Express.js generator.

Better yet, challenge yourself to use projen to create a project for you based on the generator!