SOURCE

function* demo() {
    yield 1;
    yield 2;
    yield 3;
    return 'over';

}
let it = demo();
console.log(it.next());  // { value: 1, done: false }
console.log(it.next());  // { value: 2, done: false }
console.log(it.next());  // { value: 3, done: false }
console.log(it.next());