In below code, I have used a constructor shoppingCart for the parameter CartName which identifies the Cart while loading data from the local storage. I have also used clearItems() function which is used to clear the cart and saveItems which is used for saving data items.

function shoppingCart(CartName) {
    this.cartName = cartName;
    this.clearCart = false;
    this.checkoutParameters = {};
    this.items = [];
    this.loadItems();
    var self = this;
    $(window).unload(function () {
        if (self.clearCart) {
            self.clearItems();
        }
        self.saveItems();
        self.clearCart = false;
    });
}

shoppingCart.prototype.loadItems = function () {
    var items = localStorage != null ? localStorage[this.CartName + "_items"] : null;
    if (items != null && JSON != null) {
        try {
            var items = JSON.parse(items);
            for (var i = 0; i < items.length; i++) {
                var item = items[i];
                if (item.sku != null && item.name != null && item.price != null && item.quantity != null) {
                    item = new CartItem(item.sku, item.name, item.price, item.quantity);
                    this.items.push(item);
                }
            }
        }
        catch (err) {
            // catches the errors while loading 
        }
    }
}
shoppingCart.prototype.saveItems = function () {
    if (localStorage != null && JSON != null) {
        localStorage[this.cartName + "_items"] = JSON.stringify(this.items);
    }
}