new Vue({
        el: "#app",
        data: {
            items: [
                "Sok",
                "Mleko",
                "Chleb",
                "Szampan"
            ]
        },
        methods: {
            addItem: function() {
                this.items.push( prompt("Podaj produkt") );
            },
            filterItems: function() {
                this.items = this.items.filter(function(item) {
                    return item.charAt(0) === "S";
                });
            }
        }
    });