gistfile1.js

angular
    .module('store')
    .constant('productListActiveClass', 'active')
    .controller('productListController', function ($scope, $filter, productListActiveClass) {
        var selectedCategory = null;

        $scope.selectCategory = function (categoryName) {
            selectedCategory = categoryName;
        }; 

        $scope.categoryFilterFn = function (product) {
            return !selectedCategory || product.category === selectedCategory;
        };

        $scope.getCategoryClass = function (categoryName) {
            return categoryName == selectedCategory ? productListActiveClass : '';
        };
    });

Defining AngularJS constants and importing them using dependency injection.