Multiply ASP.Net TextBox value with hidden Label value in JavaScript

Hi RichardSa,

Instead of visible false use style properties and set display attribute to none.

use innerHTML instead of value in javascript function.

Refer below modified code.

HTML

<div class="row">
    <div class="col-sm-5">
        <div class="form-group">
            <div class="input-group">
                <asp:TextBox ID="TextBox1" runat="server" CssClass="form-control" Text="" Font-Size="14pt" placeholder="10" onKeyup="calculate();" />
                <asp:Label ID="txtval" runat="server" Style="display: none" Text="10"></asp:Label>
            </div>
        </div>
    </div>
    <div class="col-sm-5">
        <div class="form-group">
            <div class="input-group">
                <asp:Label ID="LblResult" runat="server" Text="" Font-Size="14pt"></asp:Label>
            </div>
        </div>
    </div>
</div>
<script type="text/javascript">
    function calculate() {
        var txt1 = document.getElementById('TextBox1').value;
        var txt2 = document.getElementById('txtval').innerHTML;
        var myResult = parseFloat(txt1) * parseFloat(txt2);
        document.getElementById('LblResult').innerHTML = myResult;
    }
</script>

Screenshot