typescript-advanced-types

Define an event map type pairing event names with payload types, then use generics with keyof constraints so on() and emit() only accept valid events with correctly typed data. The compiler rejects mismatched payloads at compile time.

Use a conditional type with infer: type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never. This extracts the return type from 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, such as making them readonly or optional. Conditional types select a type based on a check using extends, enabling logic like extracting types or filtering union members.

Use template literal types when string values follow patterns, such as event handler names like onClick, route paths, or nested object key paths like server.host. They combine unions and string manipulation utilities like Capitalize and Uppercase.

Deeply nested conditional types and unbounded recursive types force the compiler to evaluate large type trees. Limit recursion depth, cache computed types in aliases, and prefer simpler type expressions where inference suffices.

Use unknown instead of any because unknown forces type narrowing through guards or assertions before use, preserving type safety. Reserve any for migrations where strict checking is temporarily impractical.