Constraints and default type parameters

Constraints say what a type parameter must at least be. Combined with keyof, they give you property access that stays typed.

What this lesson covers

• Constrain a parameter with extends
• Use keyof to type property access generically
• Give a type parameter a sensible default

This lesson sits in Generics, part of TypeScript for Application Developers. It assumes what came before it and leads directly into the next lesson in the module.