根据购买的产品数量更新JSON值

{
  "user_id": 12345,
  "products": [
    {
      "product_id": 101,
      "name": "Laptop",
      "quantity": 1
    },
    {
      "product_id": 102,
      "name": "Smartphone",
      "quantity": 2
    }
  ]
}

// 原始JSON字符串
let jsonString = `{
  "user_id": 12345,
  "products": [
    {
      "product_id": 101,
      "name": "Laptop",
      "quantity": 1
    },
    {
      "product_id": 102,
      "name": "Smartphone",
      "quantity": 2
    }
  ]
}`;

// 将JSON字符串转换为JavaScript对象
let user = JSON.parse(jsonString);

// 假设我们要更新product_id为101的产品数量为3
let productIdToUpdate = 101;
let newQuantity = 3;

// 查找并更新对象
user.products.forEach(product => {
  if (product.product_id === productIdToUpdate) {
    product.quantity = newQuantity;
  }
});

// 将JavaScript对象转换回JSON字符串
let updatedJsonString = JSON.stringify(user, null, 2);

console.log(updatedJsonString);

{
  "user_id": 12345,
  "products": [
    {
      "product_id": 101,
      "name": "Laptop",
      "quantity": 3
    },
    {
      "product_id": 102,
      "name": "Smartphone",
      "quantity": 2
    }
  ]
}