Surname Jansak (เจนศักดิ์ 
, Jansak 
, จันทร์ศักดิ์ ) , in the entire world, is a rare family name. The cognomen Jansak is characteristic of Slovakia, where it is quite a rare surname, Thailand, where it is a rare surname, and the United States, where it is a very rare surname. Likewise, Jansak is the forename as well as the last name.