code: function createPredicateFn(expression, comparator, matchAgainstAnyProp) {
    var predicateFn;
  
    if (comparator === true) {
      comparator = equals;
    } else if (!isFunction(comparator)) {
      comparator = function(actual, expected) {
        if (isObject(actual) || isObject(expected)) {
          // Prevent an object to be considered equal to a string like `'[object'`
          return false;
        }
  
        actual = lowercase('' + actual);
        expected = lowercase('' + expected);
        return actual.indexOf(expected) !== -1;
      };
    }
  
    predicateFn = function(item) {
      return deepCompare(item, expression, comparator, matchAgainstAnyProp);
    };
  
    return predicateFn;
  }
docs: Helper functions for `filterFilter`