Print every value within range iterator generator function javascript

Question

Iterator should print every value within range but its only printing alternate nos.

function iterator(rangeStart, rangeEnd) {
  if (rangeStart == 0 && rangeEnd == 0) {
    return null;
  }
  var iterate = function*(start = 0, end = 5, step = 1) {
    let iterationcount = 0;
    for (let i = start; i <= end; i += step) {
      yield i;
      iterationCount = i;
    }
    return iterationCount;
  }

  var values = iterate(rangeStart, rangeEnd);
  var tmp = [];


  while (values.next().value != undefined) {
    tmp.push(values.next().value);
  }
  return tmp.join(",");

}

console.log(iterator(0, 10))

expected

[0,1,2,3,4,5,6,7,8,9,10]

Result

[1,3,5,7,9,10]

You're calling `values.next()` _twice_ per loop... That's why you're skipping values. — Cerbrus, Sep 19 '22 at 14:51

trincot · Answer 1 · 2022-09-19T15:07:40.497

Every call to next will consume a value from the iterator, so the while condition is consuming a value that will therefore not get into tmp.

But... JavaScript allows you to consume values in much easier ways. For instance with Array.from or spread syntax you can collect all values from the iterator into an array.

Not your question, but:

iterationCount serves no purpose in your code, so just drop that part.
Why would the function behave differently when both range start and end are 0 than when start and end are both 10? I would remove that case. When the range end would be less than the start, it would make sense to exit, but that will happen anyway without any if statement.
The name iterator for your function is somewhat misleading, as the return value is not an iterator, but a comma separated string. I would therefore call it rangeToCsv

function rangeToCsv(rangeStart, rangeEnd) {
  var iterate = function*(start = 0, end = 5, step = 1) {
    for (let i = start; i <= end; i += step) {
      yield i;
    }
  }

  var values = iterate(rangeStart, rangeEnd);
  
  return Array.from(values).join(",");
}

console.log(rangeToCsv(0, 10))

Print every value within range iterator generator function javascript

1 Answers1