// iterators

// iterators

// any object that implements the Iterator protocol, namely having a next() method that returns an
// object with two properties:
//
// value: the next value in the sequence
// done: if true, the last value in the sequence has been consumed. If value is present, that
//     is also the iterator's return value




























function makeIterator(start, end, step) {
    let nextIndex = start;
    let count = 0;
    
    const rangeIterator = {
        next: function() {
            let result;
            if (nextIndex < end) {
                result = { value: nextIndex, done: false };
                nextIndex += step;
                count += 1;
                return result;
            }
            return { value: count, done: true };
            
        }
    };
    return rangeIterator;
}

const iterator = makeIterator(1, 10, 2);
let result = iterator.next();
while (!result.done) {
    console.log(result.value);
    result = iterator.next();
}