Javascript 加法给我 NaN

Question

我有一个 Javascript 代码，如下所示。一切都工作正常，除了净值(所有总值的总和)为 NaN。我已经使用了 parseFloat() 但结果仍然是 NaN。但我得到了所有的总值(value)。欢迎任何帮助。

window.onkeyup=function() {

  var items = document.querySelectorAll(".item");
  var itemsArray = Array.prototype.slice.call(items,0);
  var unit, rate, total, net, tax, margin, rateamount = 0;
  itemsArray.forEach(function(el){
    unit = el.querySelector('input[name="unit[]"]').value;
    rate = el.querySelector('input[name="rate[]"]').value;
    tax = el.querySelector('input[name="tax[]"]').value;
    margin = el.querySelector('input[name="margin[]"]').value;
    el.querySelector('input[id="marginrate[]"]').options[el.querySelector('input[id="marginrate[]"]').selectedIndex].text;
    var rateMargin =el.querySelector('[name="marginrate[]"]').selectedIndex;



    if (rateMargin==1) {rateamount=margin/100}
    if (rateMargin==0) {rateamount=margin}


    total = (parseFloat(unit * rate) + parseFloat(rateamount))-parseFloat(tax/100);
    alert(total);
    el.querySelector('input[name="total[]"]').value = total;
    net+= parseFloat(total);
  });

  document.getElementById('net').value=net;
}

Answer 1

您从未初始化过 net，因此当您执行 net += parseFloat(total); 时，您将向 undefined 添加一个数字，这会导致 NaN。您需要将其初始化为0。

您还应该对从输入读取的值调用 parseFloat，而不是对算术运算的结果调用(它们总是返回数字，您不需要解析它们)。

window.onkeyup = function() {

  var items = document.querySelectorAll(".item");
  var itemsArray = Array.prototype.slice.call(items, 0);
  var unit, rate, total, net = 0, tax, margin, rateamount = 0;
  itemsArray.forEach(function(el) {
    unit = el.querySelector('input[name="unit[]"]').value;
    rate = el.querySelector('input[name="rate[]"]').value;
    tax = el.querySelector('input[name="tax[]"]').value;
    margin = el.querySelector('input[name="margin[]"]').value;
    el.querySelector('input[id="marginrate[]"]').options[el.querySelector('input[id="marginrate[]"]').selectedIndex].text;
    var rateMargin = el.querySelector('[name="marginrate[]"]').selectedIndex;
    
    if (rateMargin == 1) {
      rateamount = margin / 100
    } else if (rateMargin == 0) {
      rateamount = margin
    }

    total = (parseFloat(unit) * parseFloat(rate) + parseFloat(rateamount)) - parseFloat(tax) / 100;
    alert(total);
    el.querySelector('input[name="total[]"]').value = total;
    net += total;
  });

  document.getElementById('net').value = net;
}