计算未完成下拉值 - Jquery

我是 jquery 的新手，有一个药物计算器。计算器中的值可以由用户定义，并且按预期工作。但是，我尝试使用下拉列表（SQL 查询驱动）填充字段作为替代选项。

下拉菜单

        <select name="stock_item_used" name="stock_item_used" id="stock_item_used" required>
        <option value="" disabled selected>Medication</option>
        <?php
        //Find medications
        $stmt = $conn->prepare("SELECT * from rescue_medication_trans
        LEFT JOIN rescue_medications ON rescue_medication_trans.med_profile_id = rescue_medications.medication_id
        LEFT JOIN rescue_stock_medication ON rescue_stock_medication.medication = rescue_medication_trans.med_profile_id
        WHERE rescue_medication_trans.centre_id = :centre_id
        ORDER BY common_name ASC");
        $stmt->bindParam(':centre_id', $centre_id, PDO::PARAM_INT);     
        // initialise an array for the results
        $instock = array();
        $stmt->execute();
        while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {

        $med_profile_id = $row["med_profile_id"];
        $batch_number = $row["batch_number"];
        $expiry = $row["expiry"];
        $med_common_name = $row["common_name"];
        $mcd = $row["concentration_dose"];
        $mcv = $row["concentration_volume"];
        $dose_type = $row["concentration_dose_type"];
        $volume_type = $row["concentration_volume_type"];

        //format the exp date
        $exp = new DateTime($expiry);
        $exp = $exp->format('d-m-Y');
                                            
print '<option value="' . $med_profile_id . '" data-dose="' . $mcd . '" data-volume="' . $mcv . '">' . $med_common_name . ' - ' . $mcd . '<i>' . $dose_type . '</i>  in ' . $mcv . '<i>' . $volume_type. '</i> (' . $batch_number . ' exp: ' . $exp . ') </option>'; } ?> </select> 

jquery 脚本

    <script>
    
var req_dose = 0;
var med_dose = 0;
var med_vol = 0;
var weight = 0;

$("#required_dose").change( function(){
    req_dose = $("#required_dose").val();
    calcTotals();
});
$("#medication_dose").change( function() {
    med_dose = $("#medication_dose").val();
    calcTotals();
});
$("#medication_volume").change( function() {
    med_vol = $("#medication_volume").val();
    calcTotals();
});
$("#animal_weight").change( function() {
    weight = $("#animal_weight").val();
    calcByweight();
});

var selectdose = document.getElementById("stock_item_used");
selectdose.addEventListener("change", function() {
  var optiondose = selectdose.options[selectdose.selectedIndex].getAttribute("data-dose");
  document.getElementById('medication_dose').value = optiondose;
  calcTotals();
  calcByweight();
});

var selectvol = document.getElementById("stock_item_used");
selectvol.addEventListener("change", function() {
  var optionvol = selectvol.options[selectvol.selectedIndex].getAttribute("data-volume");
  document.getElementById('medication_volume').value = optionvol;
  calcTotals();
  calcByweight();
});

function calcTotals(){
    $("#volume").text(req_dose * (med_vol / med_dose));
}
function calcByweight(){
    $("#perweight").text((req_dose * (med_vol / med_dose)) * weight);
}
</script>

行为

表格填充后，我在填充后添加了 calctotals() 以查看它是否会计算表格，但是我一直得到 NaN 或 Infinity。

如果我编辑表单字段，计算器将再次工作，但这违背了从下拉列表中填充的意义。