User Name validation

function checkname(evt){
var charCode = (evt.which != undefined) ? evt.which : evt.keyCode;
//alert(charCode);
if((charCode >= 65 && charCode <= 90) || (charCode >=97 && charCode <= 122) || charCode == 32 || charCode == 8 || charCode == 0 || charCode == 46)
return true;
return false;
}
onkeypress="return checkname(event);