code: function(fromNumber, toNumber) {
      if (typeof fromNumber === 'undefined' || typeof toNumber === 'undefined') {
        throw Error('Invalid range.');
      }
  
      var arr = [];
  
      for (var i = fromNumber; i <= toNumber; i++) {
        arr.push(i);
      }
  
      return arr;
    }
docs: Creates an array of a range of numbers.
  @param {number} fromNumber
  @param {number} toNumber
  @return {Array}