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 to do this validation in jquery?

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
} 

Answer 2

I think this is a simple logical algorithm

if ($('#field2').val() != '' && ( $('#field3').val() == '' || $('#field3').val() == '')) {
    return false;
}

Otherwise, You can find some plugins to validate form there : http://docs.jquery.com/Plugins/Validation