What TypeScript actually is

TypeScript is JavaScript with types checked before the code runs. It compiles to plain JavaScript, and at runtime there is no TypeScript left. That last point matters more than any other: types are erased when the code is built, so they cannot check anything about data arriving from a network call while your program runs. They protect you while you write, not while you run.

Understanding that boundary prevents the commonest misunderstanding. If your API returns something different from what you declared, TypeScript will not notice. You declared a promise, not a fact.

What you get in return is substantial. Your editor knows the shape of everything, so autocomplete actually works. Renaming a field updates every use. A misspelled property is an error before you open the browser. On a project with more than a few files, or more than one person, this changes the experience completely.

The cost is real too. A build step, a configuration file, and occasional fights with the type system when you are doing something clever. On a fifty line script it is not worth it. On anything that will live longer than a month, it is.

Start by renaming one file from .js to .ts. Everything still works, because valid JavaScript is valid TypeScript. Then turn on strict mode. Yes it produces errors immediately. Every one of those errors is a real thing your JavaScript was quietly doing, and fixing them is the fastest education in the language you will get.