TypeScript advanced types

What you'll learn

• How conditional types branch on type relationships
• Reading inside types with infer
• Reshaping objects with mapped types and key remapping
• Building string-shaped types with template literals
• Recursion at the type level — and where it breaks down
• Why variance shows up in callback signatures
• Reimplementing utility types from first principles
• When type-level cleverness costs more than it pays

1. 01
   Conditional types

   T extends U ? X : Y, and why unions split when you ask one question.
   18 min
2. 02
   Using infer

   Pulling a type out from inside another. Position is everything.
   17 min
3. 03
   Mapped types

   Walk every key. Add modifiers. Rename with as. Reshape on demand.
   18 min
4. 04
   Template literal types

   Strings as types, joined by interpolation. Event names, routes, CSS keys.
   18 min
5. 05
   Recursive types

   Types that call themselves. JSON, deep paths, and the depth limit.
   16 min
6. 06
   Variance, briefly

   Why a callback for Animal accepts a callback for Dog — but not the other way.
   14 min
7. 07
   Utility types from scratch

   Pick, Omit, Partial, Required, Readonly, Awaited — each a one-liner now.
   17 min
8. 08
   When to stop

   Cleverness has a price. The honest case for boring types.
   17 min