Just tested this function to validate an email..However,it does not validate the presence or absence of the dot in the email..Why this is happening and how can I fix this?

```
<script type="text/javascript">
  function isEmail(textbox){

    var reg4 =/^(\w+)@(\w+).(\w+)$/;
    if(reg4.test(textbox.value)){

            return true;
        }

    return false;
}
</script>

```