TypeScript keyof and typeof Guide

The keyof and typeof operators are fundamental tools for building dynamic, type-safe code in TypeScript.

typeof Operator#

keyof Operator#

Combining keyof and typeof#

Generic Constraints#

Indexed Access Types#

Mapped Types with keyof#

Key Remapping#

Template Literal Types with keyof#

ReturnType and Parameters#

Real-World Patterns#

Discriminated Unions with keyof#

Best Practices#

Summary#

Conclusion#

The keyof and typeof operators are powerful tools for building type-safe abstractions. Use typeof to derive types from runtime values and keyof to work with object keys as types. Combine them with mapped types, template literals, and indexed access to create sophisticated type transformations that catch errors at compile time while keeping your code DRY.