code: function filterFn() {
              if (!Array.prototype.filter) {
                  Array.prototype.filter = function (fun /*, thisArg*/) {
                      'use strict';
  
                      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];
  
                              // NOTE: Technically this should Object.defineProperty at
                              //       the next index, as push can be affected by
                              //       properties on Object.prototype and Array.prototype.
                              //       But that method's new, and collisions should be
                              //       rare, so use the more-compatible alternative.
                              if (fun.call(thisArg, val, i, t)) {
                                  res.push(val);
                              }
                          }
                      }
  
                      return res;
                  };
              }
          }
docs: From MDN site, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter