从购物车中删除商品后如何计算总金额答案

【问题标题】：how do I calculate to total amount after removing an item from the cart从购物车中删除商品后如何计算总金额
【发布时间】：2022-02-21 11:04:23
【问题描述】：

我的测试应用程序几乎完成了，但是当我从购物车中取出一个“苹果”并且数量变为 2 个时，我似乎无法改变三个苹果时的价格/总量。

这可能与构造函数类有关，但我对使用它还是比较陌生，所以我在解决这个问题时遇到了一些麻烦。

在控制台日志中，我基本上希望总金额反映苹果的数量（现在是 2 个）。


module.exports = {
    shoppingCart: function () {
        //create empty cart array
        theCart = [];
        // create two seperate versions of the same kind of object using class method 
        class Fruits {
            constructor(fruit, price, quantity) {
                this.fruit = fruit;
                this.quantity = quantity;
                this.price = price * quantity--;

            }
        }
        let fruit1 = new Fruits("Apple", 4.95, 3);       // create new object. sets the value of this
        if (fruit1.quantity === 3) {
            fruit1.quantity--;
        }

        let bothFruits = [fruit1];
        //add items to the cart
        Array.prototype.push.apply(theCart, bothFruits);

        let total = fruit1.price + " = total amount.";

        //function to add items to the cart
        function removeAllItems() {
            if (theCart.length = !0) {
                theCart = [];
            }
        }
        //removeAllItems();  
        console.log(theCart, total);
    }
}

【问题讨论】：

标签： javascript node.js arrays object

【解决方案1】：

最好将price 定义为单价，而不是总价。您可以添加更多属性，例如cost 作为水果类的总价。然后你可以添加一个方法来改变水果的数量。

module.exports = {
    shoppingCart: function () {
        //create empty cart array
        theCart = [];
        // create two seperate versions of the same kind of object using class method 
        class Fruits {
            constructor(fruit, price, quantity) {
                this.fruit = fruit;
                this.quantity = quantity;
                this.price = price;
                this.cost = quantity * price;
            }
            // add method to change fruit quantity
            changeQuantity(newQuantity) {
                this.quantity = newQuantity
                this.cost = this.price * newQuantity;
            }
        }

        let fruit1 = new Fruits("Apple", 4.95, 3);       // create new object. sets the value of this
        if (fruit1.quantity === 3) {
            fruit1.quantity--;
            fruit1.changeQuantity(fruit1.quantity);      // call the method to change the quantity
        }

        let bothFruits = [fruit1];
        //add items to the cart
        Array.prototype.push.apply(theCart, bothFruits);

        let total = fruit1.cost + " = total amount.";

        //function to add items to the cart
        function removeAllItems() {
            if (theCart.length = !0) {
                theCart = [];
            }
        }
        //removeAllItems();  
        console.log(theCart, total);
    }
}

结果

[ Fruits { fruit: 'Apple', quantity: 2, price: 4.95, cost: 9.9 } ] 9.9 = total amount.

【讨论】：