Sort array of string numbers correctly

sortStrings.js

// JsFiddle: http://jsfiddle.net/astockwell/6jxLeppm/4/

// Array.prototype.filter polyfill for <= IE8
if (!Array.prototype.filter) {Array.prototype.filter = function(fun/*, thisArg*/) {if (this === void 0 || this === null) {throw new TypeError(); } var t = Object(this); var len = t.length >>> 0; if (typeof fun !== 'function') {throw new TypeError(); } var res = []; var thisArg = arguments.length >= 2 ? arguments[1] : void 0; for (var i = 0; i < len; i++) {if (i in t) {var val = t[i]; if (fun.call(thisArg, val, i, t)) {res.push(val); } } } return res; }; }

var containsNoNumbers = function(s) {
  return s.indexOf('0') === -1;
};
var containsNumbers = function(s) {
  return !containsNoNumbers(s);
};
var getDigitsOnly = function(s) {
  return parseInt(s.replace(/\D/g, ''));
};
var correctlyOrderStringsWithNumbers = function(a, b) {
  x = getDigitsOnly(a);
  y = getDigitsOnly(b);
  return x - y;
};

var fieldStringArray = ["No Authority", "Up to 1,000", "Up to 10,000", "IT Request", "Up to 100,000", "Up to 25,000", "Up to 5,000", "Up to 50,000"];

var nonNumericOptions = fieldStringArray.filter(containsNoNumbers).sort();
// => ["IT Request", "No Authority"]

var numericOptions = fieldStringArray.filter(containsNumbers);
// => ["Up to 1,000", "Up to 10,000", "Up to 100,000", "Up to 25,000", "Up to 5,000", "Up to 50,000"]

var sortedNumericOptions = numericOptions.sort(correctlyOrderStringsWithNumbers);
// => ["Up to 1,000", "Up to 5,000", "Up to 10,000", "Up to 25,000", "Up to 50,000", "Up to 100,000"]

var sortedFieldStringArray = nonNumericOptions.concat(sortedNumericOptions);
// => ["IT Request", "No Authority", "Up to 1,000", "Up to 5,000", "Up to 10,000", "Up to 25,000", "Up to 50,000", "Up to 100,000"]