empty field validation in jquery

Question

I have 3 text fields.

The first field is the only mandatory field, but if the second field is not empty the first and third text field should not be empty.

How

Answer 1

Simple:

var set = $('input[type="text"]');
if(set.eq(0).val().length == 0 || (set.eq(1).val().length > 0 && set.eq(2).val().length == 0)) {
   //throw error
}