Question

if $('.item:last').attr('id').split('-')[1] is not undefined var liid equals that, and if it is undefined then it equals null

Answer 1

assuming that .item:last is defined:

var liid = typeof $('.item:last').attr('id').split('-')[1] != undefined ? $('.item:last').attr('id').split('-')[1] : null;

otherwise:

var liid = $('.item:last').length > 0 ? $('.item:last').attr('id').split('-')[1] : null;