ASP.NET: Text Box with ony Alphanumeric values (Javascript)

1. Use This JS
function validateAlphanumeric(e)
{ 
    var key;       
    if(window.event) 
    { 
        key = window.event.keyCode; //IE 
    } 
    else 
    { 
        key = e.which; //firefox       
    } 
    if (!((key >64 && key <=90) ||(key >96 && key <=122) ||( key ==32) ||(key >47 && key <=57) || ( key ==8)||( key == 0)||(key==127))) 
    { 
        return false; 
    }    
     else return true; 
}

2. Define your textbox as
<asp:Textbox is="myTxtBox" runat="server" onkeypress="return validateAlphanumeric(this);">