如何使用javascript函数解决卡片不变色的问题

我想实现这个功能，当

产品库存==0

时，card元素将变成灰色。我尝试使用javascript实现此功能，但它不起作用。我不知道我的代码出了什么问题。你们谁能帮我解决这个问题？如果你们能给我看一些关于如何解决这个问题的代码示例，我将不胜感激。任何帮助都将不胜感激。谢谢

这是我的PHP代码

    <?php
   $sql = "SELECT * FROM (( SELECT * FROM products) as YW1 
   LEFT JOIN 
   (SELECT product_id, SUM(quantity) totalquantity FROM ordered_items GROUP BY product_id) AS YW2 ON YW1.id = YW2.product_id) ORDER BY totalquantity DESC ";
  $query = $conn->query($sql);

  if (!mysqli_num_rows($query)) {
    echo '
      <div class="col-12">
        <div class="badge badge-danger">No Products Found</div>
      </div>
    ';
  } else {

    while ($row = $query->fetch_assoc()) {
      $product_stock =  $row['product_stock'];

    ?>
    <div class="col-lg-3 col-md-4 col-6 form-group" style="padding: 0 8px 0 8px;" >
        <div class="product-wrapper" id="productlist">
          <img class="product-img" loading="lazy" src="images/product-main/<?php echo $row['product_photo']; ?>" alt="">
          <div class="card-body" >
            <h5 class="product-title" style="min-height: 39px; text-decoration: none; width:150px; display: -webkit-box;-webkit-line-clamp: 2;-webkit-box-orient: vertical; overflow: hidden; text-align: left !important;"><?php echo $row['product_title']; ?></h5>
            <p class="product-price">RM<?php echo $row['product_price']; ?>/KG</p>
               <p style="font-size: 10px; margin-top:-10px; margin-bottom:-2px;" ><span class="text-danger" > <?php echo $sum = $row['totalquantity'] ?? 0;?> SOLD </span></p>
                <p style="font-size: 10px;" ><span class="text-success"><?php echo $row['product_stock']; ?> IN STOCK </span></p>
            <a href="product.php?cid=<?php echo $row['id']; ?>" class="btn btn-block addtocart text-center" style="text-decoration: none">View More</a>
          </div>
        </div>
    </div>
    <?php 
      }
    } 
  ?>

---

这是因为在脚本上调用product_stock变量时未定义它。 不要使用javascript代码，只需将样式直接添加到PHP代码中即可

 while ($row = $query->fetch_assoc()) {
  $product_stock =  $row['product_stock'];

 ?>
    <div class="col-lg-3 col-md-4 col-6 form-group" style="padding: 0 8px 0 8px;" >
        <div class="product-wrapper" id="productlist" style='<?php echo $product_stock == 0 ? "background-color:#d0d0d0; border:1px solid red;" : "";  ?>'>
            <img class="product-img" loading="lazy" src="images/product-main/<?php echo $row['product_photo']; ?>" alt="">
               <div class="card-body" >
                 <h5 class="product-title" style="min-height: 39px; text-decoration: none; width:150px; display: -webkit-box;-webkit-line-clamp: 2;-webkit-box-orient: vertical; overflow: hidden; text-align: left !important;"><?php echo $row['product_title']; ?></h5>
                 <p class="product-price">RM<?php echo $row['product_price']; ?>/KG</p>
                 <p style="font-size: 10px; margin-top:-10px; margin-bottom:-2px;" ><span class="text-danger" > <?php echo $sum = $row['totalquantity'] ?? 0;?> SOLD </span></p>
                 <p style="font-size: 10px;" ><span class="text-success"><?php echo $row['product_stock']; ?> IN STOCK </span></p>
                 <a href="product.php?cid=<?php echo $row['id']; ?>" class="btn btn-block addtocart text-center" style="text-decoration: none">View More</a>
               </div>
            </div>
        </div>
 <?php 
  }

while（$row=$query->fetch\u assoc（））{
$product_stock=$row['product_stock']；
?>
尝试调用你的函数getfocus（）@AliBacelonia我能知道如何调用该函数吗？getfocus（）；函数getfocus（）{//do something}@AliBacelonia是在javascript代码或php中添加的？将其添加到javascript代码中谢谢你！我的问题已经解决了！欢迎兄弟
 while ($row = $query->fetch_assoc()) {
  $product_stock =  $row['product_stock'];

 ?>
    <div class="col-lg-3 col-md-4 col-6 form-group" style="padding: 0 8px 0 8px;" >
        <div class="product-wrapper" id="productlist" style='<?php echo $product_stock == 0 ? "background-color:#d0d0d0; border:1px solid red;" : "";  ?>'>
            <img class="product-img" loading="lazy" src="images/product-main/<?php echo $row['product_photo']; ?>" alt="">
               <div class="card-body" >
                 <h5 class="product-title" style="min-height: 39px; text-decoration: none; width:150px; display: -webkit-box;-webkit-line-clamp: 2;-webkit-box-orient: vertical; overflow: hidden; text-align: left !important;"><?php echo $row['product_title']; ?></h5>
                 <p class="product-price">RM<?php echo $row['product_price']; ?>/KG</p>
                 <p style="font-size: 10px; margin-top:-10px; margin-bottom:-2px;" ><span class="text-danger" > <?php echo $sum = $row['totalquantity'] ?? 0;?> SOLD </span></p>
                 <p style="font-size: 10px;" ><span class="text-success"><?php echo $row['product_stock']; ?> IN STOCK </span></p>
                 <a href="product.php?cid=<?php echo $row['id']; ?>" class="btn btn-block addtocart text-center" style="text-decoration: none">View More</a>
               </div>
            </div>
        </div>
 <?php 
  }