cache-pattern.js

const NOT_FOUND = 'NOT_FOUND';
const cache     = {};

const db = [
    {
        id:    1,
        name:  'steve',
        email: 'steve@example.com'
    },
    {
        id:    2,
        name:  'bobby',
        email: 'bobby@example.com'
    }
];

function fetchData(id) {
    console.log('--- FETCH FROM DB ---', id);
    var item = db[id];
    if (item === undefined) {
        return NOT_FOUND;
    }
    return item;
}

function get(id, prop, forceRefresh = false) {

    var item = cache[id];

    if (forceRefresh || item === undefined) {
        item = cache[id] = fetchData(id);
    } else {
        console.log('--- FETCH FROM CACHE ---', id)
    }

    if (item === NOT_FOUND) {
        return NOT_FOUND;
    }

    if (item) {
        return item[prop];
    }
}

console.log('cache (empty)', cache);

console.log('db miss', get(3, 'name'));
console.log('db miss (cached)', get(3, 'name'));

console.log('1.name', get(1, 'name'));
console.log('1.email', get(1, 'email'));

console.log('cache (primed)', cache);

console.log('2.email', get(2, 'email'));
console.log('2.email (forceRefresh)', get(2, 'email', true));