How to create an Array sequence from one number to the next in JavaScript

upto-polyfill.js

// Works in IE9+, Chrome, Safari, Firefox, and Opera
// 
// Examples:
// (5).upTo(10) => [5, 6, 7, 8, 9, 10]
// (-1).upTo(3) => [-1, 0, 1, 2, 3]
Number.prototype.upTo = function( upper ){
  'use strict';
  var lower = this;

  if ( lower == undefined ) {
    throw new TypeError( ' this is null or not defined' );
  }

  if ( typeof upper !== 'number' ) {
    throw new TypeError( upper + ' is not a number' );
  }

  if ( lower > upper ) {
    throw new TypeError( upper + ' must be greater than your starting number' );
  }

  return Array.apply( lower, new Array( upper - lower ) ).map( function( _, index ){ return index + lower; });
};

Curious why you passed lower as the first argument (the "thisArg") to Array.apply