PROSAGA码农传奇-实时计算-用IF语句实时计算JQuery

<div class =“post-text”itemprop =“text”>
  <P>
    你的问题是
     <code>
      else
    </code>
     条件，金额
     <code>
      > 1000
    </code>
    。你正在使用
     <code>
      tax
    </code>
     未定义时的值，因此您在此行中收到错误：
  </p>
   <pre>
    <code>
      var tax = tax.value = (10);

</code>
  </pre>
  <P>
     <code>
      tax
    </code>
     也是一个整数（或调用时的字符串）
     <code>
      toFixed()
    </code>
     在它上面）永远不会有
     <code>
      value
    </code>
     属性。
  </p>
  <P>
    要解决此问题，请定义
     <code>
      tax
    </code>
     变量首先，然后修改它
     <code>
      if
    </code>
     条件：
  </p>
  <P>
  </p>
  <div class =“snippet”data-lang =“js”data-hide =“false”data-console =“true”data-babel =“false”>
    <div class =“snippet-code”>
       <pre class="snippet-code-js lang-js prettyprint-override">
        <code>
          $(function() {
  $('.amount').on('input', function() {
    var $amount = $(this);
    var amount = $amount.val()
    var $form = $amount.closest('form');
    var $tax = $form.find(".tax");
    var tax = 0;
    var $sum = $form.find(".sum");
    
    if (amount < 100) {
      tax = (1 / 10).toFixed(1);
    } else if (amount <= 1000) {
      tax = (Number(amount) * (0.5 / 100)).toFixed(1);
    } else {
      tax = 10;
    }
    
    $tax.val(tax);
    $sum.val(parseFloat(amount) + parseFloat(tax));
  });
});
        </code>
      </pre>
       <pre class="snippet-code-html lang-html prettyprint-override">
        <code>
          <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<form>
  <input type="text" name="amount" class="amount">
  <div>
    <b>tax</b>
    <p>
      <input name="tax" type="text" class="tax" readonly="readonly">
    </p>
  </div>
  <div>
    <b>total</b>
    <p>
      <input name="sum" type="text" class="sum" readonly="readonly">
    </p>
</form>
        </code>
      </pre>
    </DIV>
  </DIV>
  <P>
  </p>
  <P>
    还要注意
     <code>
      >= 100
    </code>
     在这里不需要检查
     <code>
      else
    </code>
     如果，我改变了
     <code>
      s
    </code>
     至
     <code>
      amount
    </code>
    。始终使用有意义的变量名。
  </p>
</DIV>