我如何使用JS中的reduce函数计算购物袋中商品的总价

Question

const goods = {
    "Bread": {
        price: 3,
        discount: 10,
    },
    "Milk": {
        price: 1,
        discount: 5,
    },
};

const shoppingBag = [
    { product: 'Milk', quantity: 5 },
    { product: 'Bread', quantity: 13 },
];

I need to get the sum of goods in the shoppingBag . I guess I should use reduce() but I don't know how values from goods move to shoppingBag. Could you help?

I just got keys and values from goods:

const goodsNames = Object.keys(goods);
const goodsPrices = Object.values(goods);

Answer 1

There is a certain amount of information that your question is missing that will make a full answer difficult. I've made some assumptions. The biggest assumption is that the discount is a percent that would be applied to the total of each item. To be clear, this could all be done in one reduce function as you suggest, but I find it easier to understand if broken up into smaller functions. I'm using map to take each product in the shopping cart and return the total amount for that product. Reduce is used at the end to sum up the total of all of the products in the cart.

 const goods = { "Bread": { price: 3, discount: 10, }, "Milk": { price: 1, discount: 5, }, }; const shoppingBag = [ {product: 'Milk', quantity: 5}, {product: 'Bread', quantity: 13}, ]; console.log( shoppingBag .map(item => { // get the items pricing information by looking it up in the object based off of its key. var itemPricing = goods[item.product]; // calculate the gross total amount for the item before applying the discount var itemGrossTotal = item.quantity * itemPricing.price; // make the percentage into a decimal and apply the discount to the gross total return itemGrossTotal * ((100 - itemPricing.discount)/100); }) // sum the discounted price of all of the products .reduce((item1, item2) => item1 + item2, 0) );

Answer 2

I have an ideal. First need to collection in map and have to do reduce

    var total = shoppingBag.map(item=>{
        return goods[item.product].price*item.quantity;
    }).reduce((total,num)=>{
        return total+num;
    })
console.log(total)

Answer 3

you can use this

update the calculation as need

shoppingBag.reduce((accumulator, current) => {
// current is the current iteration of the array

   const itemPricingObj = goods[current.product];

// do the math as you want
// but i will just get total Price

   return accumulator + ((itemPricingObj.price * current.quantity) - (itemPricingObj.discount * itemPricingObj.price ))

}, 0); // 0 is the initial value of the accumulator

Answer 4

Assuming discount is in percentage, this can do the job

function calculate() {
    const goods = {
        "Bread": {
            price: 3,
            discount: 10,
        },
        "Clothes": {
            price: 40,
            discount: 8
        },
        "Milk": {
            price: 1,
            discount: 5,
        },
    };
    
    
    const shoppingBag = [
        { product: 'Bread', quantity: 13 },
        { product: 'Milk', quantity: 5 },
        { product: 'Clothes', quantity: 5 },
    ];

    const totalSum = shoppingBag.reduce((prev, current) => {
        const totalPrice = goods[current.product].price * current.quantity;
        const discount = goods[current.product].discount;
        const netPrice = totalPrice * (100 - discount) / 100;
        return prev + netPrice;
    }, 0);

    console.log(totalSum);

}

Answer 5

I feel this would be a lot cleaner, what do you think?

const getDiscountedPrice = (price, discount) => {
  return Math.round(
    price * (1 - (discount/100))
  );
}

const calculateTotalPrice = (shoppingBag, goods) => shoppingBag.reduce((totalPrice, bagItem) => {
  const { product, quantity} = bagItem;
  const productDetails = goods[product];
  // Check if the item in the `shoppingBag` exists in `goods`
  if (productDetails) {
    const { price, discount } = productDetails;
    totalPrice += (quantity * getDiscountedPrice(price, discount));
  }
  return totalPrice;
}, 0);

console.log('Total amount pending: ', calculateTotalPrice(shoppingBag, goods));