Introduction

TypeScript: only what you can't write code without

If you already know JS, there's no need to start from zero. No history of the language here, no decorators, no three screens of conditional types. There's the contract, narrowing, generics and an honest fetch. Then separate lessons on each topic.

10 lessons99 min

To the first lesson Cheatsheet now

Topics, each as its own lesson

01What changes if you know JSDemo

TypeScript is JavaScript plus a contract. At runtime there are no types.

02Inference: when you don't need to write the type

The compiler already knows the type. An annotation is needed when it can't guess.

03Objects, optional, readonly

The shape of an object is the main contract in an app.

Type the input. TS often infers the output itself.

05Unions and narrowing

The main TypeScript skill. Everything else derives from it.

06type vs interface

Almost the same thing. The difference is in a couple of cases, not in religion.

One function, the type passes all the way through. Not abstraction for its own sake.

08Utility types

Seven of them cover almost all everyday work.

09any, unknown, never, as

Four words that make TS either help you or lie to you.

10Async, fetch, real code

How to type what comes from a server without fooling yourself.

0/10 topics open. This is the course intro, not the whole course on one page.

In the knowledge base

Reference pages for the technologies on this topic: who maintains them, when to use them and what interviews ask.

TypeScript