TypeScript Setup for Node.js with VS Code

TypeScript is a superset of JavaScript that provides optional static typing along with type inference. It also supports modern JavaScript features, which makes it similar to the Babel project.

TypeScript makes working with JavaScript more enjoyable. One of the biggest advantages of using TypeScript is the IntelliSense feature, which provides a rich development environment with contextual code completions, hover info and method signature information.

At the same time TypeScript is not necessary to write great software. Most of the articles about TypeScript picture the language as the necessity. This is not true. In software, most problems come from errors in specifications and architectural mistakes.

Types improve the coding experience on the lower level and at the micro scale. They greatly help with writing particular lines of code by providing a stricter, thus slightly safer coding environment.

It is difficult to estimate the actual benefits, but adopting TypeScript is not something that will change your software practice in dramatic ways. There are even prominent voices saying you shouldn't use types at all.

I think this is exactly backwards, types often cripple larger codebases. #Clojure https://t.co/2eJIQsmRrR

— stuarthalloway (@stuarthalloway) September 27, 2019

Personally I find great pleasure in using TypeScript, to the extend of not willing to write regular JavaScript anymore.

Simplest TypeScript Snippet

Let's start with the simplest TypeScript code snippet, which is also not idiomatic. In other words, it's a syntaxtically correct piece of code which doesn't follow the common coding practice.

let message: string = "Hello World"

TypeScript allows us to specify the type for the message variable as string. This type annotation describes a range of values that a particular variable (or constant) can take, or a particular function can return. With TypeScript we can now explicitly specify the value constrains in our code. It leads to a stricter control, which is a good thing.

Types, however, reduce the code flexibility. That's one of the reasons why there is no consensus in the debate of static versus dynamic typing. At the end of the day, it boils down to the personal preference and experience.

Type Inference

So what's wrong with this short snippet? The piece of TypeScript is not idiomatic, because TypeScript not only allows us to specify type, but is also smart enough to guess the types based on how particular variable or function is used in the code - this feature is known as type inference.

The TypeScript compiler looks at our code and infers the ranges of values for our variables, constans or functions. Type inference is something you should use as much as possible. Usually, the compiler knows better than you what types to use. Therefore, in idiomatic TypeScript, the code from above should be written as follows:

let message = "Hello World"

Funny enough, it looks like a regular JavaScript. As a general rule you should not specify types in the assignments as those can be easily inferred by the TypeScript compiler; on the other hand, you should explicitly provide types for the function parameters.

An HTTP Server in TypeScript

Let's now write a simple HTTP server in Node.js using TypeScript to see how VS Code supports TypeScript out of the box. You may know that VS Code is actually written in TypeScript, but the editor also provides a feature called the Automatic Types Aquisition.

With the Automatic Types Aquisition VS Code automatically downloads the type definitions for the packages you use in your code. This makes using TypeScript even more convenient and straighforward.

Let's initialize a TypeScript project:

mkdir typescript-with-zaiste
cd typescript-with-zaiste
npm init --yes
npm install -D typescript
tsc init

and let's consider the following snippet stored in the ~app.ts~ file:

import http, { IncomingMessage, ServerResponse } from 'http';
 
const handler = (request: IncomingMessage, response: ServerResponse) => {
  response.end('Hello, World');
}
 
http
  .createServer(handler)
  .listen(8080, () => console.log('started'));

The Automatic Types Acquisition being enabled by default in VS Code, I can simply type the . (the dot) after the response variable to see all possible fields and methods of that object along with their documentation.

This is possible thanks to those type definitions. I don't need to switch back and forward between the documentation of the http module. Everything is in one place which streamlines the coding.

Types in Plain JavaScript

The http is a core module from Node.js and Node.js is not written in TypeScript. Thus, there is no information about types in it. Plenty of popular NPM packages are still written using JavaScript as well.

In order to provide type information in those cases, there is a special project called DefinitelyTyped. The Automatic Type Aquisition feature in VS Code aquires the type information from that project. In our example, we relied on the ~@types/node~ to have this information for the http module from Node.js.

It is a good practice to include those types definitions explicitly in your project using the devDependencies of the package.json. Those using editors other than VS Code will be able then to benefit form the type definitions as well.

npm install -D @types/node

A TypeScript project must be first compiled (or transpiled) into JavaScript before we can run with Node.js. This transpilation process is done using the ~tsc~ command line tool that comes with the ~typescript~ package.

npm install -D typescript

In order to have a more streamlined process we can instruct the TypeScript compiler to constantly watch our files using the --watch option and automatically recompile once there are changes within them.

TypeScript with VS Code

VS Code recognizes TypeScript projects by the presence of the tsconfig.json and conveniently provides the appropriate build tasks. The compilation can be trigger directly using the Command Palette and seamlessly run using the UI of the editor - there is no need to switch between the terminal and the editor anymore.

We can also specify the default build task in VS Code to further simplify the whole process and have it conveniently under the build command via the editor wide key binding.

This setup works for well for regular, command-line applications which we run to do a specific tasks. Once it's done, they finish. In Node.js, however, we also build web servers - long running processes that accept requests and return responses. This slightly troubles the setup of a TypeScript application. We not only need to transpile our code from TypeScript to JavaScript, but we also need to reload our Node.js server instance once this compilation is done and for each such change in our files.

There are many solutions for this problem. We could use nodemon to restart both TypeScript compilation and the server once there are changes in our files - this is not optimal though, especially for bigger projects. We could also use a tool called `ts-node-dev~ which is slightly smarter and shares the TypeScript compilation between restarts. There is, however, a better solution.

PM2 for Restarts in Development

The JavaScript ecosystem is insanely rich to the point to be easily overwhelming. I prefer to keep the dependencies to minimum and to reuse what is already there. For that reason we will use the pm2 tool, which is the Node.js standard for running Node.js processes in production. This tool also provides a development mode as the pm2-dev command. Let's use it instead of adding another dependency.

"scripts": {
  "dev": "pm2-dev app.js"
}

Let's run the dev script directly using the tasks feature in VS Code in addition to the already running TypeScript compiler process via tsc --watch. From now on any change in the app.ts will be automatically recompiled by TypeScript and then quickly reloaded by the pm2 tool.

TypeScript makes writing JavaScript more enjoyable. It reduces the probability of making typos while the type system constrains the area for mistakes.

We also simplified and sped up the development process by eliminating the need to switch between the editor and the terminal - everything is now in one place, directly accessible from VS Code.

That's a perfect TypeScript setup for Node.js with VS Code, indeed!