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Giwa Jossy
Giwa Jossy

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Understanding TypeScript & Using it in Your Node Environment.

I struggled with this concept a lot, but let me save you the stress, and explain as simply as I can.

Typescript is just a secure way of writing JavaScript code. Do not get confused by the fancy terminologies people throw around it.

The good news is, if you know JavaScript, you already know ~90% of Typescript. The additional layer only forces you to be a lot more intentional about your variables and data types.


Why Typescript?

Simple answer? To catch errors early in your editor.
Typescript detects silly bugs at runtime; bugs you probably wouldn’t notice until it’s too late when using pure JavaScript.


Here's sample JavaScript code:

let id = 1
let company = "GYRO Design Lab"
let isPublished = true
let mandem = ["Dexter", "Mide", "Emmy"]

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But the unfortunate thing here is that, at some point later in your code, the variable company - for instance, could be re-assigned to a value of an entirely different data type, which would be unexpected behavior.
Sadly, JavaScript will not throw an error, and this poses a compounding threat to your App.
Thankfully, popular code editors like VScode now use Typescript under the hood, to spot errors like these.


Sample Typescript code

let id: number = 10 
let company: string = "GYRO Design Lab"
let isPublished: boolean = true

// Here, the variable "x" can later be re-assigned a value of different datatype
let x: any = "Hello" 

// This is an array of numbers. This - "Number[]", tells the system that the variable "ids" is expected to be an array of numbers. So if you try to push a string in the array, you will get an error.
let ids: number[] = [1,2,3,4,5] 

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As you can see, with Typescript, you have to explicitly define your Types.

When creating an object, for instance, you get to create an interface that defines the shape of your object;

// interface declaration
interface User {
    Name: string;
    Id: number

// Javascript object which conforms to the shape of the interface. 
const user: User = {
    Name: "Janet",
    Id: 0
// Typescript will warn you if it doesn't match.
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So what exactly happens under the hood?

Typescript code transpiles to JavaScript, which runs anywhere JavaScript runs: In a browser, on NodeJS, and in your apps.

“Transpiling is a specific term for taking source code written in one language and transforming into another language that has a similar level of abstraction” - stackoverflow.

When setting up your Typescript+NodeJS project, your entire project files are usually in a folder, including your Typescript [.ts] files.

However, your browser will not run .ts files, this is why the Typescript engine automatically generates a new project folder containing the transpiled version of our entire project, which we can now run and test.


Now let's create a simple NodeJS App, and configure Typescript.

  • Initialize your project
    npm init -y

  • Install Typescript as dev dependency.
    npm install -D typescript

  • Generate a configuration file - tsconfig.json
    npx tsc --init

Now open the tsconfig.json file, you will see a bunch of commented-out codes; no worries, look for the properties below, and make these changes to them.
Note: Some of the properties below are commented-out by default in the tsconfig.json file, you will have to uncomment them.

”Target": "es6”
”rootDir": "./src” "src" will be the name of your project folder
”outDir": "./build” "build" is the auto-generated folder that will holds your transpiled files.

  • In your package.json file, add the following tags into your "scripts" key like so;
"scripts" : {
    "build" : "tsc"
    "dev": "npm run build && node build/index.js"
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"build" : "tsc" is responsible for transpiling the Typescript codes to JavaScript, and "dev": "npm run build && node build/index.js" runs the program when you type "npm run dev" in you console.

We have successfully integrated Typescript to our app. Now let's see it in action.

  • At the moment, your root directory should contain /node_modules, package.json.lock, package.json, and a tsconfig.json file. Create a new folder - src. Your first Typescript file goes in here.

  • create an index.ts file inside the src folder.

  • Paste the entire typescript snippet shown at the beginning of this article, into your index.ts

  • Finally run npm run dev in your terminal. You will notice a newly generated folder /build, which contains a transpile version of your Typescript code.

Hope you find this helpful.

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