javascript - HTML 表单输入 javascript 自动求和 支付总价

Question

我有以下代码来销售产品，如果我应用折扣，它可以工作，如果我应用税，则同样，每单位的所有价格(数量 1)都有效，但如果我更改数量，则支付的总价不起作用

我需要的是自动填充以便稍后将以下字段保存到 mysql:

default price per unit (comming from mysql) = working
apply taxes or not per unit = working
apply discount per unit = working
price per unit after discount and after taxes = working

如果我将数量从 1 更改为 2 o 3 等，则需要支付的总价 = 不起作用这必须通过乘以每单位税后按数量支付的价格来自动填充=不起作用

这是代码

<table width="339" border="0" cellpadding="0">
  <tr>
    <td width="98">Pay taxes?</td>
    <td width="115">Make Discount?</td>
    <td width="118">Default unit price</td>
     <td>Quantity</td>
  </tr>
  <tr>
    <td>
      <select name="taxes" class="select">
        <option value="0" selected>no taxes</option>
        <option value="19">19% taxes</option>
      </select>
    </td>
    <td>
      <select name="discount" class="select">
        <option value="0" selected>no discount</option>
        <option value="5">5% discount</option>
        <option value="10">10% discount</option>
        <option value="20">20% discount</option>
      </select>
    </td>
    <td>
      <input type="text" name="cost" class="input140" value="1000">
    </td>
    <td><input type="text" name="quantity" value="1"></td>
  </tr>
  <tr>
    <td>Unit price after discount</td>
    <td>Tax per unit</td>
    <td>Total Price per unit</td>
     <td>Total Price to pay per quantity</td>
  </tr>
  <tr>
    <td><input type="text" name="price" value="1000"></td>
    <td><input type="text" name="ttaxes" value="0"></td>
    <td><input type="text" name="total" value="1000"></td>
    <td><input type="text" name="totaltopay" value="1000"></td>
  </tr>
 </table><script>
/**
 * Elements
 */
var taxes    = document.getElementsByName('taxes')[0];
var discount = document.getElementsByName('discount')[0];
var cost     = document.getElementsByName('cost')[0];
var price    = document.getElementsByName('price')[0];
var ttaxes   = document.getElementsByName('ttaxes')[0];
var total    = document.getElementsByName('total')[0];


/**
 * Calculations
 */
function updateInput() {
  price.value = cost.value - (cost.value * (discount.value / 100));
  ttaxes.value = (price.value * (taxes.value / 100));
  var sum = parseFloat(price.value) + parseFloat(ttaxes.value);
  total.value = sum.toFixed(0);
}


/**
 * Event Listeners
 */
taxes.addEventListener('change', updateInput);
discount.addEventListener('change', updateInput);
cost.addEventListener('change', updateInput);
cost.addEventListener('keyup', updateInput);
</script>

这是演示 fiddle

https://fiddle.jshell.net/63dkvgs5/

我需要的图像示例

Answer 1

您忘记添加数量!

var quantity = document.getElementsByName('quantity')[0];
quantity.addEventListener('keyup', updateInput);

并更新计算:

var sum = (parseFloat(price.value) + parseFloat(ttaxes.value)) * quantity.value;

fiddle :https://fiddle.jshell.net/praveenscience/v6spxoqv/