One question that you might have right now is why does the index file have a different extension? That is, why is it .tsx and not .ts? To answer these questions, we have to change our mental image of the extension slightly and talk about why React uses .jsx files and not .js (the .tsx version is the TypeScript equivalent of .jsx).
These JSX files are extensions of JavaScript that get transpiled to JavaScript. If you were to try and run them as is in JavaScript, then you would get runtime errors if they contained any of these extensions. In traditional React, there is a transpilation phase that takes the JSX file and converts it to JavaScript by expanding out the code to standard JavaScript. Effectively, this is a form of the compilation phase that we get from TypeScript anyway. With TypeScript React, we get the same end result where the TSX file ultimately...
