Allow only Numeric Value in TextBox using JavaScript

<script type="text/javascript">

    var specialKeys = new Array();
    specialKeys.push(8); //Backspace
    
    function Allow_Numeric(e) 
    {
       var keyCode = e.which ? e.which : e.keyCode
       var ret = ((keyCode >= 48 && keyCode <= 57) || specialKeys.indexOf(keyCode) != -1);
       document.getElementById("error").style.display = ret ? "none" : "inline";
       return ret;
    }
    </script>

<input type="text" id="text1" onkeypress="return Allow_Numeric(event);"/>
<span id="error" style="color: Red; display: none">* Input digits (0 - 9)</span>