TypeScript in Depth

The route

1. Inference is the point

   Letting the compiler do the work, and what an annotation is really for.

   You board here
   95 min
2. Narrowing and the discriminated union

   Modelling states so the impossible ones will not compile.

   95 min
3. Generics that read well

   Type parameters and constraints, and knowing when a generic is overkill.

   95 min
4. The type-level toolkit

   Conditional and mapped types, keyof and template literals — used sparingly, on purpose.

   95 min
5. Types at the boundary

   Validating what arrives from an API, and where `unknown` beats `any`.

   95 min
6. Configuring a real codebase

   The strict flags, module resolution, and living with third-party types.

   95 min

A look at the teaching

// Flags let you express nonsense — loading AND an error AND data:
type Bad = { loading: boolean; error?: string; data?: Course };

// A discriminated union cannot:
type State =
  | { status: "loading" }
  | { status: "error"; message: string }
  | { status: "ready"; data: Course };

function render(s: State) {
  if (s.status === "error") return s.message;    // narrowed
  if (s.status === "ready") return s.data.title; // narrowed
  return "Loading…";
}

Who is driving