js_from_like_2015.js

'use strict';
var Foo = {
    *[Symbol.iterator]() {
        for (let [idx, val] of this.nums.entries()) {
            yield label => `${label}: ${val}
                (${idx+1} / ${this.nums.length})`;
        }
    },
    bar([x = 1, y = 2, ...nums] = []) {
        this.nums = [x, y, ...nums];
    }
};

Foo.bar([10,20,30,40,50]);

for (let f of Foo) {
    console.log( f("Foo") );
}

/* Output:
Foo: 10
                (1 / 5)
Foo: 20
                (2 / 5)
Foo: 30
                (3 / 5)
Foo: 40
                (4 / 5)
Foo: 50
                (5 / 5)
*/