typescript-advanced-types

Define an event map type mapping event names to payload types, then use generics with keyof constraints so on() and emit() enforce the correct payload type per event. The Skill provides a complete TypedEventEmitter implementation using mapped types over the event map.

Use a conditional type with the infer keyword: type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never. This extracts the return type R from any function type passed as the generic parameter.

Mapped types iterate over an existing type's properties to transform them, such as making all properties readonly or optional. Conditional types select a type based on a condition using the extends keyword, enabling type-level logic like extracting or filtering types.

Use template literal types when you need string types that follow patterns, such as event handler names like onClick, dot-notation paths like server.host, or string transformations with Uppercase, Lowercase, and Capitalize utilities.

Common pitfalls include over-using any, ignoring strict null checks, creating overly complex types that slow compilation, missing discriminated union narrowing, and circular type references. Deeply nested conditional types can also degrade compiler performance.