ip, cómo escribir la expresión regular del nombre de dominio

var ip=/((25[0-5])|(2[0-4]\d)|(1\d\d)|([1-9]\d)| \d)(\.((25[0-5])|(2[0-4]\d)|(1\d\d)|([1-9]\d)|\d)){ 3}

/;

var dominio=/[a-zA-Z0-9][-a-zA-Z0-9]{0,62}(\.[ a-zA-Z0-9][-a-zA-Z0-9]{0,62})+\.?

/;

var cadena=valor entrante;

if(!ip.test(string)){

//TODO

}else if(!domain.test(string)){< / p>

//TODO

}