How TypeScript compiles to JavaScript - Quick Revision & Summary

Recall & Review

beginner

What is the main purpose of compiling TypeScript to JavaScript?

TypeScript code is converted into JavaScript because browsers and Node.js can only run JavaScript. The compiler removes TypeScript-specific features like types and outputs plain JavaScript.

beginner

What file extension does TypeScript use and what does it produce after compilation?

TypeScript files use the .ts extension. After compilation, they produce JavaScript files with the .js extension.

beginner

How does the TypeScript compiler handle type annotations during compilation?

Type annotations are used only during development for checking errors. The compiler removes all type annotations in the output JavaScript because JavaScript does not support types.

beginner

What command is commonly used to compile a TypeScript file named app.ts?

The command is tsc app.ts. This runs the TypeScript compiler and creates a JavaScript file named app.js.

intermediate

Can TypeScript compile to different versions of JavaScript? How?

Yes. You can set the target JavaScript version (like ES5, ES6) in the tsconfig.json file or with the --target option. This controls the JavaScript features used in the output.

What does the TypeScript compiler remove when converting to JavaScript?

A Variable names

B All functions

C Comments only

D Type annotations and interfaces

The compiler removes type annotations and interfaces because JavaScript does not support them.

Which file extension is generated after compiling a TypeScript file?

A .ts

B .tsx

C .js

D .json

TypeScript files (.ts) compile into JavaScript files (.js).

Which command compiles a TypeScript file named main.ts?

A node main.ts

B tsc main.ts

C npm main.ts

D compile main.ts

The TypeScript compiler command is tsc, so tsc main.ts compiles the file.

Why do we compile TypeScript to JavaScript?

A Because JavaScript cannot run TypeScript directly

B To add more types to the code

C To make the code run faster

D To convert JavaScript to TypeScript

Browsers and Node.js only understand JavaScript, so TypeScript must be compiled to JavaScript to run.

How can you control the JavaScript version output by the TypeScript compiler?

A Using the <code>--target</code> option or <code>tsconfig.json</code>

B By renaming the output file

C By changing the file extension to .js

D By running JavaScript code first

The --target option or tsconfig.json file lets you specify the JavaScript version for the output.

Explain in your own words why TypeScript code needs to be compiled to JavaScript before running in a browser.

Think about what browsers can run and what TypeScript adds.

Describe the role of the TypeScript compiler and what happens to type annotations during compilation.

Focus on what the compiler does with types and the output.