Definitions for generator functions range() and irange()

irange.js

/**
 * Gives a range of numbers starting with `start` and ending before or at
 * `boundary` while incrementing each time by `increment`.
 * @param {number} start
 *   The number at which position to start.
 * @param {number} boundary
 *   The number at which position to stop (inclusive).
 * @param {number=} increment
 *   Defaults to `1`.  The amount to increment by between each iteration.
 * @yields {number}
 *   The next value in the range.
 * @example
 *   console.log([...irange(1, 10)]); // [1,2,3,4,5,6,7,8,9,10]
 * @example
 *   console.log([...irange(10, 1, -1)]); // [10,9,8,7,6,5,4,3,2,1]
 */
function irange(start, boundary, step=1) {
  return range(start, boundary + step, step);
}

range.js

/**
 * Gives a range of numbers starting with `start` and ending before `boundary`
 * while incrementing each time by `increment`.
 * @param {number} start
 *   The number at which position to start.
 * @param {number} boundary
 *   The number at which position to stop (non-inclusive).
 * @param {number=} increment
 *   Defaults to `1`.  The amount to increment by between each iteration.
 * @yields {number}
 *   The next value in the range.
 * @example
 *   console.log([...range(1, 10)]); // [0,1,2,3,4,5,6,7,8,9]
 * @example
 *   console.log([...range(10, 1, -1)]); // [10,9,8,7,6,5,4,3,2]
 */
function* range(start, boundary, increment=1) {
  let remaining = Math.ceil((boundary - start) / increment);
  if (!isFinite(remaining)) remaining = 0;
  for (; 0 < remaining--; ) {
    yield start;
    start += increment;
  }
}