如果購物車中已存在商品 - reactjs，如何更新購物車數量？

Question

在此代碼中，而不是顯示“產品已添加到購物車”。 警告消息，如果購物車中已有商品，我想更新購物車數量，請幫幫我。

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

我在這里對你的變量是什么樣子做了一些假設，但一般來說，這是你需要的：

 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

嘗試類似於以下方法的方法：

   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]);
  }
};