Application Development

TypeScript

The type system on top of JavaScript, taught against the real compiler: inference, unions, narrowing, generics, and typing the messy data that arrives from an API.

The course project

Typed Explorer

The Knowledge Explorer from the React course, converted to TypeScript, with every response validated at the boundary rather than assumed.

course

12 modules · 24 lessons

Each module ends with a practice test, a graded build, and a step of the course project.

Part I: The Idea

Why Types

Mistakes found while typing, rather than while somebody is using the page.

Inference and the Basic Types

Let the compiler work it out, and annotate only the boundaries.

Part II: Shapes

Functions

Where the annotations earn their keep.

Objects and Interfaces

Describing the shape of your data, once.

Part III: Proving Things

Unions and Narrowing

Most real values are one of several things. Narrowing is how you prove which.

Discriminated Unions

The single most useful pattern in the language, and it fixes the four states.

Part IV: Reuse

Generics

Working with many types without losing track of which one you were given.

Utility Types

Deriving types from other types, so they cannot drift apart.

Part V: The Boundary

Untrusted Data

The most important module here. Types are erased, so nothing checks what arrived.

TypeScript with React

Props, state, events, and the four states one last time.

Part VI: In Practice

Configuration and Migration

The settings that matter, and how to add types to something that already exists.

The Typed Explorer

Requirements and acceptance criteria. No instructions.

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