typescript-advanced-types

Define an event map type pairing event names with payload shapes, then use a generic class keyed on that map so on() and emit() enforce correct payload types per event. The compiler rejects mismatched payloads at call sites.

Use a conditional type with infer: type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never. This extracts the return type of any function type, and the same infer pattern works for parameters, array elements, and promise values.

Mapped types iterate over an existing type's keys to transform properties, like Partial or Readonly. Conditional types select a type based on a check using extends, enabling logic like extracting types or distributing over unions.

Use unknown instead of any because unknown forces type narrowing through guards before use, preserving type safety. The any type disables all checking and can hide runtime errors.

Deeply nested or recursive conditional types force the compiler to evaluate many type instantiations, increasing check time. Mitigate this by simplifying type logic, caching intermediate type aliases, and limiting recursion depth.