How TypeScript compiles to JavaScript

Introduction

TypeScript code is turned into JavaScript so browsers and servers can understand and run it.

When you write TypeScript code and want to run it in a web browser.

When you build a Node.js app using TypeScript and need JavaScript output.

When you want to check your TypeScript code for errors before running it.

When you want to use modern TypeScript features but still support older JavaScript environments.

Syntax

Typescript

tsc filename.ts

tsc is the TypeScript compiler command.

You run it in the terminal to convert .ts files into .js files.

Examples

This compiles the app.ts file into app.js.

Typescript

tsc app.ts

This compiles app.ts and keeps watching for changes to recompile automatically.

Typescript

tsc --watch app.ts

This compiles src/index.ts and puts the JavaScript output into the dist folder.

Typescript

tsc --outDir dist src/index.ts

Sample Program

This TypeScript code defines a text variable and prints it.

When compiled, it becomes plain JavaScript that browsers can run.

Typescript

const greet: string = 'Hello, friend!';
console.log(greet);

Important Notes

The compiled JavaScript removes all TypeScript types because JavaScript does not use types.

You can configure the compiler with a tsconfig.json file to customize output.

Errors in TypeScript code are caught during compilation before running the JavaScript.

Summary

TypeScript code is converted to JavaScript using the tsc command.

This process removes types and creates code that browsers and servers can run.

Compiling helps catch errors early and supports using new TypeScript features safely.