如果购物车中已经存在商品 - reactjs，如何更新购物车数量？

Question

在此代码中，而不是显示“产品已添加到购物车”。提示信息，如果购物车中已经存在商品，我想更新购物车数量，请帮帮我。

const addToCart = (id) => {
    const check = cart.every((item) => {
      return item.id !== id;
    });
    if (check) {
      const cartData = products.filter((el) => {
        return el.id === id;
      });
      setCart([...cart, ...cartData]);
    } else {
      alert('The product has been added to cart.');
    }

Answer 1

我在这里对您的变量的外观做出一些假设，但一般来说，这是您需要的：

const products = [{id: 1, name: 'Prod 1'}, {id: 2, name: 'Prod 2'}, {id: 3, name: 'Prod 3'}, {id: 4, name: 'Prod 4'}]
const cart = [{id: 1, name: 'Prod 1', quantity: 1}, {id: 4, name: 'Prod 4', quantity: 1}];

const addToCart = (id) => {
    const check_index = cart.findIndex(item => item.id === id);
    if (check_index !== -1) {
      cart[check_index].quantity++;
      console.log("Quantity updated:", cart);
    } else {
      cart.push({...products.find(p => p.id === id), quantity: 1})
      console.log('The product has been added to cart:', cart);
    }
}

addToCart(4)

Answer 2

尝试类似于下面的方法：

   const addToCart = (id) => {
  const check = cart.every((item) => {
    return item.id !== id;
  });
  const cartData = products.filter((el) => {
    return el.id === id;
  });
  if (check) {
    setCart([...cart, ...cartData]);
  } else {
    const itemForCountIncrease = cart.find((item) => item.id == id);
    itemForCountIncrease.count += 1;
    setCart([...cart.filter((item) => item.id != id), itemForCountIncrease]);
  }
};