javascript - 如何解决这个问题 Uncaught TypeError: Cannot read property 'addEventListener' of null

Question

如何解决这个问题我的代码在 foreach 循环中工作，然后它只能在第一行工作，而另一行不能工作。显示错误“未捕获的类型错误：无法读取 null 的属性 'addEventListener'”我可以修复吗？

<script type='text/javascript'>

        function sum() {
       var txtFirstNumberValue = document.getElementById('txt1').value;
       var txtSecondNumberValue = document.getElementById('txt2').value;
       var txtforeNumberValue = document.getElementById('txt4').value;
       if (txtFirstNumberValue == "")
           txtFirstNumberValue = 0;
       if (txtSecondNumberValue == "")
           txtSecondNumberValue = 0;
      if (txtforeNumberValue == "")
            txtforeNumberValue = 0;

       var result = parseInt(txtFirstNumberValue) - parseInt(txtSecondNumberValue);
       var result_add = parseInt(txtSecondNumberValue) + parseInt(txtforeNumberValue);
       if (!isNaN(result)) {
           document.getElementById('txt3').value = result;
           document.getElementById('txt5').value = result_add;
       }
   }
   </script>

<td>
                          <label for="quantity">หน้าร้าน</label>
                          <input type="hidden" id="txt1" value="{{ $product->quantity_offline}}"  onkeyup="sum();" />
                          <input type="text" class="form-control" name="quantity_offline" id="txt3" value="{{ $product->quantity_offline}}"  onkeyup="sum();" />
                             
                          </td> 
                          
                          <td>
                          <label for="quantity">โอน&lt;/label>
                          <img src="{{ asset('img/right-arrow.png') }}">
                          <input type="text" id="txt2" class="form-control" name="quantity_offline" onkeyup="sum();" />
                               

                          <td>
                          <label for="quantity">ออนไลน์&lt;/label>
                          <input type="hidden" id="txt4" value="{{ $product->quantity }}"  onkeyup="sum();" />
                              <input type="text" id="txt5" class="form-control" name="quantity" value="{{ $product->quantity }}"  onkeyup="sum();" />
                              
                          </td>

标签： javascript