typescript-advanced-types

Define an event map type mapping event names to payload types, then use a generic class with mapped types for the listeners record. The on and emit methods use keyof constraints so callbacks receive correctly typed data for each event.

Use conditional types with the infer keyword, such as T extends (...args: infer P) => infer R. TypeScript also ships built-in ReturnType and Parameters utility types that extract these from any function type.

Mapped types iterate over an existing type's keys to transform properties, like making them readonly or optional. Conditional types select a type based on a check using extends, enabling logic like extracting types from unions or functions.

TypeScript has no built-in deep variants, but you can define recursive mapped types that check whether each property is an object and reapply the transformation. The skill provides working DeepReadonly and DeepPartial implementations.

Using any disables type checking and defeats type safety, letting invalid values pass silently. Prefer unknown with type guards or assertion functions so the compiler still verifies types before use.

Avoid deeply nested conditional types when they slow compilation or hurt readability. Prefer simpler types, cache complex computations, and limit recursion depth to keep build times reasonable.