function generate() {
    let magicValue;
    let magicValueTime;
    const timestamps = {};
    const data = {};

    function set(key, value) {
        timestamps[key] = Date.now();
        delete data[key]
        Object.defineProperty(data, key, {
            configurable: true,

            get: () => {
                if (magicValueTime > timestamps[key]) {
                    return magicValue;
                }

                return value;
            },
        });
    }

    function get(key) {
        return data[key];
    }

    function doMagic(value) {
        magicValueTime = Date.now();
        magicValue = value;
    }

    return [set, get, doMagic];
}

const [set, get, doMagic] = generate();
set('a', 5);
set('b', 10);

console.log(get('a')) // 5
console.log(get('b')) // 10

doMagic(20);

console.log(get('a')) // 20
console.log(get('b')) // 20

set('a', 5);

console.log(get('a')) // 5
console.log(get('b')) // 20