A first project with ExpressoTS

The Developer-Friendly TypeScript Framework for Server-Side Applications - 8/25/2023

10 min read


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ExpressoTS is a new developer-friendly TypeScript framework for Server-Side Applications. It’s currently built on top of Express, easy to get a new developer on board, light and easy project structure, two different project structure supported (opinionated and non opinionated version), supports MVC, non MVC, architecture. The opinionated template was built on top of clean architecture, you will see concepts embedded in the opinionated template such as entities, useCases, repositories and providers.


The logo correctly indicates the speed of the framework.

Setting Up Your First ExpressoTS Project

Ah, the first step to any great journey in the world of coding—a proper setup. Trust me, nobody wants to get lost before even starting the adventure. So, let’s cut the chit-chat and dive right in.

Installation of ExpressoTS CLI

You’ve got two routes here, and the destination is the same, a functional ExpressoTS environment. Your first option is to install the ExpressoTS CLI globally:

pnpm i -g @expressots/cli

Got limited commitment issues? No worries, you can also use dlx to run the CLI without installing it globally. Ah, the wonders of a one-night stand with a CLI!

pnpx @expressots/cli new expressots-first-project

Configuration Wizard

After running the command, you’re greeted by a friendly (albeit text-based) wizard 🧙‍♂️.

[🐎 Expressots]
? Project name expressots-first-project
? Package manager pnpm
? Select a template Non-Opinionated :: A simple ExpressoTS project.
? Do you want to create this project? Yes

Fill out the form wisely but don’t overthink it. For this tutorial, I’m going with the “Non-Opinionated” template because, it will give us a shallower learning curve in the start.

Getting Comfy in Your New ExpressoTS Home 🏡

So you’ve set up your new ExpressoTS project. Awesome! Time to get inside the engine room and take a look under the hood.

cd expressots-first-project

You’re now in the root folder, and if you’re curious about what comes packed by default, run a quick tree command.

@expressots/tests/expressots-first-project via  v16.19.0
 tree -I node_modules -a
├── .eslintrc.js
├── expressots.config.ts
├── .gitignore
├── jest.config.ts
├── package.json
├── pnpm-lock.yaml
├── .prettierrc
├── src
│   ├── app.container.ts
│   ├── app.controller.ts
│   ├── app.module.ts
│   ├── app.usecase.ts
│   └── main.ts
├── test
│   └── app.usecase.spec.ts
└── tsconfig.json
3 directories, 16 files

There you go! These are the files you’ll be living with.

Customizing Your Prettier Preferences

You’ve got your own coding style—don’t we all? You can tweak the .prettierrc file to your heart’s content.

  "singleQuote": false,
  "trailingComma": "all",
  "endOfLine": "auto",
  "tabWidth": 2

Let’s Take a Quick Tour of package.json

A glance at the scripts section in package.json tells you all you need to know to get things up and running.

 cat package.json | jq ".scripts"
  "prebuild": "rm -rf ./dist",
  "build": "tsc -p",
  "dev": "tsnd ./src/main.ts",
  "prod": "node ./dist/main.js",
  "test": "jest",
  "test:watch": "jest --watchAll",
  "test:cov": "jest --coverage",
  "format": "prettier --write \"src/**/*.ts\" \"test/**/*.ts\"",
  "lint": "eslint \"src/**/*.ts\" --fix"

Here, you’ve got your usual suspects: build, dev, test, and more.

Format All The Things!

Before diving into development, let’s keep it neat. The format script will handle that.

pnpm format

Running in Dev Mode

And finally, the moment you’ve been waiting for—fire up the dev server and see your app come to life!

@expressots/tests/expressots-first-project via  v16.19.0
 pnpm dev
[INFO] ts-node-dev ver. 2.0.0 (using ts-node ver. 10.9.1, typescript ver. 4.9.5)
Application version not provided is running on port 3000 - Environment: development

Making Your First Request in ExpressoTS 🌐

Time for a Little Hello!

You’ve been through the house tour, you’ve feng shui’d your .prettierrc and got your scripts all figured out. Now what? Well, how about actually seeing your app in action?

Using HTTPie for Your First GET Request

For this demonstration, we’re going to use HTTPie — the cURL for the 21st century. But like, way more readable. Here’s how to send your first GET request to http://localhost:3000.

@expressots/tests/expressots-first-project via  v16.19.0
 http :3000

Bam! You should see a response like:

HTTP/1.1 200 OK
Hello Expresso TS!

Congrats! You just made your server say hello.

Anatomy of the “Hello Expresso TS!” 🦴

Alright, let’s dissect that "Hello Expresso TS!" message. How does this simple string pass through layers of TypeScript files to make it to your browser? Spoiler: It’s not magic; it’s just well-structured code.

The Starting Point: src/main.ts

This is where the baton is picked up. Here, we import the essential parts from ExpressoTS and set up the initial application instance. Simple enough.

import "reflect-metadata";
import { AppInstance, ServerEnvironment } from "@expressots/core";
import { container } from "./app.container";
async function bootstrap() {
  AppInstance.listen(3000, ServerEnvironment.Development);

The Container: src/app.container.ts

Think of this as the backstage, where everyone gets ready for the show. It’s where the application container is configured with your custom modules.

import { AppContainer } from "@expressots/core";
import { AppModule } from "./app.module";
const appContainer = new AppContainer();
const container = appContainer.create([AppModule]);
export { container };

The Module: src/app.module.ts

Modules in ExpressoTS group related functionalities. Here, it’s as simple as importing the AppController.

import { CreateModule } from "@expressots/core";
import { AppController } from "./app.controller";
const AppModule = CreateModule([AppController]);
export { AppModule };

The Controller: src/app.controller.ts

This is the conductor of our orchestra. It’s responsible for handling HTTP requests and directing traffic. In this case, it’s just saying, "Hello Expresso TS!".

import {
} from "inversify-express-utils";
import { Response } from "express";
import { AppUseCase } from "./app.usecase";
class AppController extends BaseController {
  constructor(private appUseCase: AppUseCase) {
  execute(@response() res: Response) {
    return res.send(this.appUseCase.execute());

The Use Case: src/app.usecase.ts

Here’s where the actual "Hello Expresso TS!" lives.

import { provide } from "inversify-binding-decorators";
class AppUseCase {
  execute() {
    return "Hello Expresso TS!";

“Hello, Who?” Changing the Default Response 🖊️

Got bored of the usual "Hello Expresso TS!"? Let’s give it a personal touch. To do that, we only need to venture into the src/app.usecase.ts file. See, this is the beauty of a well-structured codebase; you don’t have to jump through hoops to make a simple change.

The Tweak: src/app.usecase.ts

One line change. That’s it. Here we just swap out the text to "Hello from <Daniel::Boll>".

class AppUseCase {
  execute() {
    return "Hello from <Daniel::Boll>";

The Reload: Auto-refresh FTW

As soon as you save that change, the development server detects this update and reloads itself. No manual effort required. Ah, the joys of modern development.

[INFO] Restarting: /../@expressots/tests/expressots-first-project/src/app.usecase.ts has been modified
Application version not provided is running on port 3000 - Environment: development

The Result: Let’s Talk to the Server Again

Run the command, and voila! The updated greeting is now served hot, right from your server.

Hello from <Daniel::Boll>

Tuning Port via Environment Variables 🎛️

Great, we’re diving into environment-specific configuration! This makes the application flexible and easier to deploy in various environments.

Port Configuration in src/main.ts

We modify the AppInstance.listen() method to get the port from the environment variable PORT. If PORT is not available, it defaults to 3000.

import "reflect-metadata";
import { AppInstance, Environments, ServerEnvironment } from "@expressots/core";
import { container } from "./app.container";
async function bootstrap() {
    Number(process.env.PORT) ?? 3000,

Environment Checks

Adding Environments.checkAll(); ensures that our environment is sound before the application starts. This is a proactive approach, helping to catch issues early.

Feedback on Missing .env and Variables

When you don’t provide the .env file or the PORT variable, ExpressoTS kindly informs you. This is immensely helpful for debugging and avoids “silent failures.”

[timestamp] [core-api] [env-validator-provider] info: Environment variable PORT is not defined.

Creating .env and Updating Port

  1. We start by creating an empty .env file, simulating a missing PORT variable.
  2. The server informs us that the PORT variable is missing.
  3. We then set PORT to 3001 in the .env file.

Verify New Port

Finally, when the server restarts, it picks up the PORT value from .env. As expected, the server now runs on port 3001.

[INFO] ts-node-dev ver. 2.0.0 (using ts-node ver. 10.9.1, typescript ver. 4.9.5)
Application version not provided is running on port 3001 - Environment: development

Fantastic, we now have a flexible, environment-aware application. This is a crucial step for making the application ready for various stages of deployment, like development, testing, and production. 🌐

Utilizing the CLI for Efficient Development 🛠️

Changing to Opinionated Mode

Switching the project to be opinionated is as simple as modifying expressots.config.ts:

import { ExpressoConfig, Pattern } from "@expressots/core";
const config: ExpressoConfig = {
  sourceRoot: "src",
  scaffoldPattern: Pattern.KEBAB_CASE,
  opinionated: true,
export default config;

Scaffolding Services with the CLI

The Expresso CLI is versatile and can assist in creating various resources. To understand its capabilities:

 pnpx @expressots/cli generate --help
[🐎 Expressots]
expressots generate [schematic] [path]
Scaffold a new resource
  schematic  The schematic to generate                   [string] [choices: "usecase", "controller", "dto", "service", "provider", "entity"]
  path, d    The path to generate the schematic                                                                                     [string]
  method, m  HTTP method                                                         [string] [choices: "get", "post", "put", "patch", "delete"]
  -h, --help  Show command help                                                                                                    [boolean]

For our scenario, we’ll generate a service named user/create, which will scaffold a controller, use case, and provider.

 pnpx @expressots/cli generate service user/create
[🐎 Expressots]
  [controller]   create.controller.ts created! ✔️
  [usecase]      create.usecase.ts created! ✔️
  [dto]          create.dto.ts created! ✔️
  [module]       user.module created! ✔️
  [container]    UserModule added to app.container.ts! ✔️

This automates a plethora of tasks:

  • Creating necessary files
  • Adding the new module to app.container.ts
  • Extending the existing app.module.ts

The changes are reflected in src/app.container.ts:

const container = appContainer.create([AppModule, UserModule]);

Structuring the Service Directory

By default, without a trailing slash in the CLI command, the scaffold looks like this:

 tree src/user
├── create.controller.ts
├── create.dto.ts
└── create.usecase.ts

However, adding a trailing slash creates a more modular folder structure, better suited for extending functionalities such as CRUD operations.

After reverting previous changes:

 pnpx @expressots/cli generate service user/create/

The new structure is:

 tree src/user
├── create
   ├── create.controller.ts
   ├── create.dto.ts
   └── create.usecase.ts
└── user.module.ts

This fine-tuned control over the codebase structure is immensely helpful for managing large projects efficiently.

Completing the User Creation Feature 🛠️

Updating DTOs

Your DTOs specify the shape of incoming and outgoing data:

interface ICreateRequestDTO {
  name: string;
  age: number;
interface ICreateResponseDTO extends ICreateRequestDTO {
  id: string;
export { ICreateRequestDTO, ICreateResponseDTO };

Adjusting the Controller

The controller now listens to POST requests and forwards the payload to the use case:

import { BaseController, StatusCode } from "@expressots/core";
import {
} from "inversify-express-utils";
import { Response } from "express";
import { CreateUseCase } from "./create.usecase";
import { ICreateRequestDTO, ICreateResponseDTO } from "./create.dto";
class CreateController extends BaseController {
  constructor(private createUseCase: CreateUseCase) {
    @requestBody() payload: ICreateRequestDTO,
    @response() res: Response
  ): ICreateResponseDTO {
    return this.callUseCase(
export { CreateController };

Updating the Use Case

The use case is now a singleton, maintaining a state of user records:

import { provideSingleton } from "@expressots/core";
import { ICreateRequestDTO, ICreateResponseDTO } from "./create.dto";
import crypto from "crypto";
interface User extends ICreateResponseDTO {}
class CreateUseCase {
  private users: User[] = [];
  constructor() {}
  execute(payload: ICreateRequestDTO): ICreateResponseDTO {
    if (this.users.find((user) => === {
      throw new Error("User already exists");
    const user: User = {
      id: crypto.randomUUID(),
    return user;
export { CreateUseCase };

Testing the Functionality

First attempt at creating a user:

 http POST :3000/user/create name=John age=20
  "age": "20",
  "id": "4e1ed6e3-e4a6-48b6-bb77-390fc331b5b6",
  "name": "John"

Second attempt fails as expected:

 http POST :3000/user/create name=John age=20
  "error": "User already exists"

Wrapping Up 🎉

Although this approach may not align 100% with best practices, it provides a functional example. The Opinionated Architecture extends this example into a more robust setup, which includes repositories, entities, and more.

Thanks for following along! Hope this was insightful and stay tuned for more! 👋