The tsc Compiler

Let's set up a simple TypeScript Node.js application on your local machine. Follow these steps to get started:

Step 1 - Install tsc/TypeScript Globally

First, install TypeScript globally using npm.

npm install -g typescript

Step 2 - Initialize a Node.js Project with TypeScript

Create a new directory for your Node.js application and initialize it with TypeScript.

mkdir node-app
cd node-app
npm init -y
npx tsc --init

These commands will create your project directory and initialize it with package.json and tsconfig.json.

Step 3 - Create a a.ts File

Create a new TypeScript file named a.ts and add the following code:

const x: number = 1;
console.log(x);

Step 4 - Compile the .ts File to a .js File

Use the TypeScript compiler to compile your TypeScript file into JavaScript.

tsc -b

Step 5 - Check the Generated a.js File

Open the generated a.js file. You'll see that it contains plain JavaScript code with no type annotations.

var x = 1;
console.log(x);

Step 6 - Modify a.ts to Assign x to a String

Change a.ts by converting const to let and assigning x to a string:

let x: number = 1;
x = "something other than number";  // This will cause a type error
console.log(x);

Step 7 - Recompile the Code

Compile the code again with the TypeScript compiler:

tsc -b

You will see errors in the console indicating type mismatches. Additionally, notice that no a.js file is generated this time due to the type errors.