Creates a span of numbers as an array.

range-and-span.js

/**
 * Creates an array with the range of numbers going from `first` and ending but
 * not including `limit` depending on the specified step value.
 * @name range
 * @param {number} first
 *   First number that should appear in the returned array.
 * @param {number} limit
 *   The number just outside of the range which serves as a limit for the last
 *   number in the returned array.
 * @param {number=} opt_step 
 *   Defaults to `1` if not given or if `0` or `NaN` is specified.  The
 *   difference between each subsequent number in the returned array.
 * @returns {Array}
 *   An array containing the sequence of numbers starting at `first` and ending
 *   at a number before `limit` with each number being separated by `opt_step`.
 */

/**
 * Creates an array with the span of numbers going from `first` and ending at
 * `last` if possible depending on the specified step value.
 * @name span
 * @param {number} first
 *   First number that should appear in the returned array.
 * @param {number} last
 *   Last number that should appear in the returned array.
 * @param {number=} opt_step 
 *   Defaults to `1` if not given or if `0` or `NaN` is specified.  The
 *   difference between each subsequent number in the returned array.
 * @returns {Array}
 *   An array containing the sequence of numbers starting at `first` and ending
 *   at `last`.  If `first` is less than `last` and `opt_step` is less than `0`
 *   or if `last` is less than `first` and `opt_step` is greater than `0` an
 *   empty array will be returned.
 */

// Creates both the range() and span() functions.
eval('range span='.replace(/(\w+)(.)/g,'function $1(a,c,b){2>arguments.length&&(c=a,a=0);b=+b||1;for(var d=[],e=0>b?-1:1;0<$2e*(c-a);a+=b)d.push(a);return d}'));

range.uncompressed.js

/**
 * Creates an array with the range of numbers going from `first` and ending but
 * not including `limit` depending on the specified step value.
 * @name range
 * @param {number} first
 *   First number that should appear in the returned array.
 * @param {number} limit
 *   The number just outside of the range which serves as a limit for the last
 *   number in the returned array.
 * @param {number=} opt_step 
 *   Defaults to `1` if not given or if `0` or `NaN` is specified.  The
 *   difference between each subsequent number in the returned array.
 * @returns {Array}
 *   An array containing the sequence of numbers starting at `first` and ending
 *   at a number before `limit` with each number being separated by `opt_step`.
 */
function range(first, limit, opt_step) {
  if (arguments.length < 2) {
    limit = first;
    first = 0;
  }
  opt_step = +opt_step || 1;
  let result = [];
  for (let mult = opt_step < 0 ? -1 : 1; mult * (limit - first) > 0; first += opt_step) {
    result.push(first);
  }
  return result;
}

span.uncompressed.js

/**
 * Creates an array with the span of numbers going from `first` and ending at
 * `last` if possible depending on the specified step value.
 * @name span
 * @param {number} first
 *   First number that should appear in the returned array.
 * @param {number} last
 *   Last number that should appear in the returned array.
 * @param {number=} opt_step 
 *   Defaults to `1` if not given or if `0` or `NaN` is specified.  The
 *   difference between each subsequent number in the returned array.
 * @returns {Array}
 *   An array containing the sequence of numbers starting at `first` and ending
 *   at `last`.  If `first` is less than `last` and `opt_step` is less than `0`
 *   or if `last` is less than `first` and `opt_step` is greater than `0` an
 *   empty array will be returned.
 */
function span(first, last, opt_step) {
  if (arguments.length < 2) {
    last = first;
    first = 0;
  }
  opt_step = +opt_step || 1;
  let result = [];
  for (let mult = opt_step < 0 ? -1 : 1; mult * (last - first) >= 0; first += opt_step) {
    result.push(first);
  }
  return result;
}