SOURCE

function counter(n) {
    return {
        get count() {
            let nPlus = n++;
            console.log('print get count():', nPlus);
            return nPlus;
        },
        set count(m) {
            if (m > n) n = m;
            else throw Error('count can only be set to a larger value');
        }
    }
}
let c = counter(1000);
c.count;
c.count;
c.count=2000;
c.count;
c.count=2000;