js购物车数量加减代码

<div>
  <button id="decrease">-</button>
  <input type="text" id="quantity" value="1">
  <button id="increase">+</button>
</div>

// 获取元素
const decreaseBtn = document.getElementById('decrease');
const increaseBtn = document.getElementById('increase');
const quantityInput = document.getElementById('quantity');

// 减少数量
decreaseBtn.addEventListener('click', () => {
  let quantity = parseInt(quantityInput.value);
  if (quantity > 1) {
    quantity--;
    quantityInput.value = quantity;
  }
});

// 增加数量
increaseBtn.addEventListener('click', () => {
  let quantity = parseInt(quantityInput.value);
  quantity++;
  quantityInput.value = quantity;
});

quantityInput.addEventListener('input', () => {
  let quantity = parseInt(quantityInput.value);
  if (isNaN(quantity)) {
    quantityInput.value = 1;
  }
});