iterator_plain.js

function makeIterator(n) {
    return {
      cnt: n,
    
      next: function() {
        this.cnt--;
        return {value: this.cnt, done: this.cnt < 0};
      },
    };
}

it = makeIterator(30);

while (true) {
  const {value, done} = it.next();
  if (done) {
    break;
  } 
  console.log(value);
}