Allowed Only Number to Type in TextBox using JavaScript

Allowed Only Number to type in Text box using JavaScript.

Firstly add function in Onkeypress event of textbox,

<asp:TextBox ID="txtChallanNo" runat="server" CssClass="Input" Text="0" AutoPostBack="true" onkeypress="return isNumber(event);"></asp:TextBox>

Add JavaScript code,

<script type="text/javascript" language="javascript">
    function isNumber(evt)
    {
        debugger;
        evt = (evt) ? evt : window.event;
        var charCode = (evt.which) ? evt.which : evt.keyCode;
        if (charCode > 31 && (charCode < 48 || charCode > 57))
        {
            alert("Please Enter Only Number");
            return false;
        }
        else
        {
            return true;
        }
    }
</script>