iterator.js

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

it = makeIterator(30);

for (value of it) {
    console.log(value);
}