typescript-advanced-types

Define an event map type mapping event names to payload types, then use generics with mapped types so on() and emit() methods infer the correct payload type per event. The compiler then rejects mismatched event names or payloads.

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 argument.

Interfaces are preferred for object shapes because they produce better error messages and support declaration merging. Type aliases are more flexible for unions, conditional types, mapped types, and other complex type computations.

TypeScript has no built-in deep variants, but you can define them recursively with mapped and conditional types that check whether each property is an object, array, or function before transforming it.

The unknown type forces explicit type checking or narrowing before a value can be used, while any disables all type checking. Using unknown with type guards preserves compile-time safety without losing flexibility.

Avoid deeply nested conditional types when they slow compilation or become unreadable. Prefer simpler types, cache complex computations in named aliases, and limit recursion depth in recursive type definitions.