What is the template literal type key remapping in TypeScript?

Key remapping in mapped types (TypeScript 4.1) uses the as clause to transform property names during mapping. Syntax: type Mapped = { [K in keyof T as NewKeyType]: T[K] }. Generate getter methods: type Getters<T> = { [K in keyof T as `get\${Capitalize<string & K>}`]: () => T[K] };. For interface User { name: string; age: number; }, Getters<User> produces { getName(): string; getAge(): number; }. Filter properties during mapping by using never: type NoFunctions<T> = { [K in keyof T as T[K] extends Function ? never : K]: T[K] }; — remapping to never removes that key from the result. Combine with template literals for prefix/suffix transformations: type Prefixed<T, P extends string> = { [K in keyof T as `\${P}\${string & K}`]: T[K] };. Key remapping enables advanced type transformations like generating event handler types, API endpoint types, and form field types from data model types.