doubeng9567 2019-05-07 06:31
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如何在第三个输入框中添加两个输入值并显示？ 用这样简单的JavaScript帮助我在哪里错了[重复]

This question already has an answer here:

1)I want to add the values of two input boxes and show it in the third input. It shows an error

2)Error: Uncaught TypeError: Cannot read property 'value' of null at sum (js.php:21) at HTMLButtonElement.onclick (js.php:12)

<!DOCTYPE html>
<html>

  <head>
    <title>JavaScript</title>
    <script type="text/javascript">
      function sum() {
        var val1 = document.getElementById('val1').value;
        var val2 = document.getElementById('val2').value;
        var sum = val1 + val1;
        document.getElementById('total').value = sum;
      }

    </script>
  </head>

  <body>
    <input type="text" name="val1"><br><br>
    <input type="text" name="val2"><br><br>
    <input disabled name="total" value=""><br><br>
    <button type="button" onclick="sum()" name="btn">Add</button>
  </body>

</html>

I expected the sum of two inputs but it shows nothing.

</div>
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  • doumicheng6732 2019-05-07 06:36
    关注

    You should have the attribute id for the controls which you are referencing in your code with getElementById(). You also have to convert the string value to number to perform the arithmetic operation:

    function sum(){
  var val1 = document.getElementById('val1').value;
  var val2 = document.getElementById('val2').value;
  var sum = Number(val1) + Number(val2);
  document.getElementById('total').value = sum;
}
    <input type="text" name="val1" id="val1"><br><br>
<input type="text" name="val2" id="val2"><br><br>
<input name="total" id="total" value=""><br><br>
<button type="button" onclick="sum()" name="btn">Add</button>

    </div>
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
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