typescript-advanced-types

Generics let you parameterize functions with type variables like function identity<T>(value: T): T. Follow the Golden Rule: if a type parameter appears only in the signature and not in the return type or body, replace it with a plain union type instead.

Define an event map type mapping event names to payload types, then use a generic class with mapped types over keyof T for the listeners registry. The on and emit methods constrain event names and payload types through generic keys.

Conditional types select a type based on a check using T extends U ? X : Y, while mapped types transform object types by iterating over keys with [P in keyof T]. They are often combined for filtering or remapping properties.

TypeScript uses structural typing by default, but you can simulate nominal typing with branded types like string & { _brand: 'url' }. Combine with a type guard to validate values before assigning the brand.

Omit<T, K> does not constrain K to keyof T, so misspelled keys pass silently. Use StrictOmit<T, K extends keyof T> = Omit<T, K> to make TypeScript report an error when the key does not exist.

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