map-values-1.ts

function MapValues<K extends string, S, D>(
    source: { [k in K]: S },
    mapper: (value: S, key: K, src: { [k in K]: S }) => D
): { [k in K]: D } {
    const dest = {} as { [k in K]: D };
    
    for (let key of Object.keys(source) as K[]) {
        dest[key] = mapper(source[key], key, source)
    }

    return dest;
}

map-values.js

export const mapValues = (source, mapper) => Object.keys(source).reduce(
  (dest, key) => {
    dest[key] = mapper(source[key], key, source);
    return dest;
  },
  {}
);

map-values.ts

const MapValues = <K extends string, S, D>(
    source: { [k in K]: S },
    mapper: (value: S, key: K, src: { [k in K]: S }) => D
): { [key in K]: D } => (Object.keys(source) as K[]).reduce(
    (dest: { [k in K]: D }, key: K): { [k in K]: D } => {
        dest[key] = mapper(source[key], key, source);
        return dest;
    },
    {} as { [key in K]: D}
);

interface ICar {
    price: number;
    name: string;
}

const carSource: Record<string, ICar> = {
    first: {
        name: "BMW",
        price: 100000,
    },
    second: {
        name: "Mersede",
        price: 200000,
    },
};

const MULTIPLIER = 2;

let multiplyCarPrice = (car: ICar): ICar => ({
    ...car,
    price: car.price * MULTIPLIER,
});

function mapValues<T>(source: Record<string, T>, mapper: (T) => T): Record<string, T> {
    return Object.keys(source).reduce((dest, key): Record<string, T> => {
        dest[key] = mapper(source[key]);
        return dest;
    }, {});
}

mapValues(carSource, multiplyCarPrice);