data model using mobservables

gistfile1.js

function Article(name, price) {
    mobx.extendObservable(this, {
        name: name,
        price: price
    });
}

function ShoppingCartEntry(article) {
    mobx.extendObservable(this, {
        article: article,
        amount: 1,
        price: function() {
            return this.article ? this.article.price * this.amount : 0;
        }
    });
}

function ShoppingCart() {
    mobx.extendObservable(this, {
        entries: [],
        total: function() {
            return this.entries.reduce(function(sum, entry) {
                return sum + entry.price;
            }, 0);
        }
    });
}