Shorthand for multiple OR expressions in if statement

you could use an array

if(["","com","net","co","org","info","biz"].indexOf(tld) > -1) {
     // do something
}

or if you are using jquery :

$.inArray(tld, ["com","net","co","org","info","biz"])

REF - Performance of OR operation ( || ) vs inArray()

Use a regexp:

if ( /^(com|net|co|org|info|biz)$/i.test(tld) ) {
    // do something
}