counter2.js

function counter(n) {  // Function argument n is the private variable
    return {
        // Property getter method returns and increments private counter var.
        get count() { return n++; },
        // Property setter doesn't allow the value of n to decrease
        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            // => 1000
c.count            // => 1001
c.count = 2000;
c.count            // => 2000
c.count = 2000;    // !Error: count can only be set to a larger value