Question

The regex below works nice except I need only one dot (.) at the end for nameserver. For example if user submit ns1.hello.com there will be error. Accepted format is with dot at the end like this ns1.hello.com. Help me please. Thank you.

    <script type="text/javascript">



function validSubdomain() {

    var re = /^[a-zA-Z0-9][a-zA-Z0-9.-]+\.$/;



    var val = document.getElementById("nameserver").value;

    var val2 = document.getElementById("nameserver2").value;



if(val == '' && val2 == ''){

     alert("Please fill in the name server"); 

     document.forms['namaform'].elements['nameserver'].focus();

     return false; 

} 



if(val == ''){

     alert("Please fill in the name server 1"); 

     document.forms['namaform'].elements['nameserver'].focus();

     return false; 

} 

if(val2 == ''){

     alert("Please fill in the name server 2"); 

     document.forms['namaform'].elements['nameserver2'].focus();

     return false; 

} 



var parts = val.split('.');

var parts2 = val2.split('.');

if (parts.length < 3) 

{ alert('invalid nameserver format') 

document.forms['namaform'].elements['nameserver'].focus();

return false;

}

else if (parts2.length < 3) 

{ alert('invalid nameserver 2 format') 

document.forms['namaform'].elements['nameserver2'].focus();

return false;

}









if( !re.test(val)) {

    alert("invalid nameserver 1 format");

    return false;

}

else if( !re.test(val2)) {

    alert("invalid nameserver 2 format");

}

else{namaform.submit();}







}

</script>

Answer 1

Two things wrong with:

if(re.test(val && val2)) {  
    alert("valid format"); 
} 
if(!re.test(val && val2)) { 
    alert("invalid format"); 
} 

First of all, have you never heard of else? It’s there specifically so you don’t have to repeat a test in the negative.

Second, you are trying to && together the two string and then passing the resulting boolean to re.test(). Since a boolean converts to the string "true" or "false" it will never ever match.

Change to:

if( re.test(val) && re.test(val2)) {
    alert("valid format");
}
else {
    alert("invalid format");
}

Also note that your regex is wrong. It would accept a..b as input, which is clearly not valid. Try this instead:

var re = /^([a-z0-9-]+\.)+[a-z]{2,3}\.$/i;

This will broadly match most domains with unlimited number of subdomain levels, provided there’s a . at the end.

EDIT to disallow - at the front of a section:

var re = /^([a-z0-9][a-z0-9-]*\.)+[a-z]{2,3}\.$/i;