@{
    ViewData["Title"] = "Create";
} 
<div class="text-center">  
    <h2 class="display-4">Order creation</h2> 
</div> 
<form method="post"> 
    <div class="row">   
        <div class="col-4">Dress:</div>   
        <div class="col-8">    
            <select id="dress" name="dress" class="form-control" asp-items="@(new SelectList(@ViewBag.Dresses,"ID", "DressName"))"></select>   
        </div>  
    </div>  
    <div class="row">   
        <div class="col-4">Quantity:</div>   
        <div class="col-8"><input type="text" name="count" id="count" /></div>  
    </div>  
    <div class="row">   
        <div class="col-4">Total:</div>   
        <div class="col-8"><input type="text" id="sum" name="sum" readonly /></div>  
    </div>  
    <div class="row">   
        <div class="col-8"></div>   
        <div class="col-4"><input type="submit" value="Create" class="btn btn-primary" /></div>  
    </div> 
</form>  
<script>
    $('#dress').on('change', function () 
    { 
        check(); 
    }); 

    $('#count').on('change', function () 
    { 
        check(); 
    }); 

    function check() 
    { 
        var count = $('#count').val(); 
        var dress = $('#dress').val(); 
        if (count && dress) 
        { 
            $.ajax({ 
                method: "POST", 
                url: "/Home/Calc", 
                data: { count: count, dress: dress }, 
                success: function (result) 
                { 
                    $("#sum").val(result); 
                } 
            }); 
        }; 
    }
</script>