ReplaceProps in TypeScript

ReplaceProps.ts

// https://stackoverflow.com/questions/53011500/how-to-replace-properties-using-mapped-types-in-typescript
// https://twitter.com/inamiy/status/1278511811025711104

type ReplaceProps<T, From, To> = {
    [K in keyof T]: K extends keyof From
        ? T[K] extends From[K]
            ? K extends keyof To
                ? To[K]
                : T[K]
            : T[K]
        : T[K]
}

interface From {
    foo: string
    bar?: boolean
    baz: () => number
}

interface To {
    foo(x: number): boolean
    bar(): void
    baz: string
}

interface Input {
    foo?: string // matches `From`
    bar: boolean // matches `From`
    baz: number // doesn't match `From`
    aNumber: number
    aMethod(): void
}

type Output = ReplaceProps<Input, From, To>

// type Output = {
//     foo?: (x: number) => boolean;
//     bar: () => void;
//     baz: number;
//     aNumber: number;
//     aMethod: () => void;
// }

type ReplacePropsSimple<T, To> = {
    [K in keyof T]: K extends keyof To ? To[K] : T[K]
}

type Output2 = ReplacePropsSimple<Input, To>

// type Output2 = {
//     foo?: (x: number) => boolean;
//     bar: () => void;
//     baz: string;
//     aNumber: number;
//     aMethod: () => void;
// }