TypeScript design patterns

What you'll learn

• Making illegal states unrepresentable with discriminated unions
• Branded and opaque types for ids that won't mix up
• Exhaustiveness checking with the never type
• Result types as a clear alternative to throwing
• Builder and fluent APIs that guide you through required steps
• The unknown contract — narrowing before use

1. 01
   Make illegal states unrepresentable

   The classic loading flag bug. Why a discriminated union beats a bag of optional fields.
   16 min
2. 02
   Branded and opaque types

   Stop mixing UserId and OrderId. A zero-runtime trick that makes the compiler help.
   14 min
3. 03
   Readonly everywhere

   readonly properties, readonly arrays, as const. Where shallow ends and deep begins.
   14 min
4. 04
   Exhaustiveness with never

   assertNever in a switch default. Add a new case and the compiler tells you what to fix.
   15 min
5. 05
   Builder patterns and method chaining

   Fluent APIs that refuse to compile until you call the required steps.
   17 min
6. 06
   Result types

   Return failure instead of throwing it. When this beats try/catch, and when it doesn't.
   14 min
7. 07
   Tagged unions for events and actions

   Reducer actions, event handlers, command objects. One pattern that scales.
   16 min
8. 08
   The unknown problem

   unknown vs any. Why one keeps you safe and the other quietly lies.
   14 min