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.

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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

01

Why Types

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

02

Inference and the Basic Types

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

Section project · coming soon

Type a Small Program

Add types to a plain JavaScript program and let the compiler find a bug.

Part II: Shapes

03

Functions

Where the annotations earn their keep.

04

Objects and Interfaces

Describing the shape of your data, once.

Section project · coming soon

Model the Domain

Describe real records with types, unions and optional fields.

Part III: Proving Things

05

Unions and Narrowing

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

06

Discriminated Unions

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

Section project · coming soon

Make Bad States Impossible

Design types so invalid data can't be represented.

Part IV: Reuse

07

Generics

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

08

Utility Types

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

Section project · coming soon

A Typed Utility Library

Write generic helpers you can reuse across projects.

Part V: The Boundary

09

Untrusted Data

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

10

TypeScript with React

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

Section project · coming soon

Validate What Comes In

Check data from an API at the boundary, before trusting it.

Part VI: In Practice

11

Configuration and Migration

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

12

The Typed Explorer

Requirements and acceptance criteria. No instructions.

Section project · coming soon

Convert an App

Migrate a small app to TypeScript without breaking it.

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