how swagger.json works with nodejs?

I've one nodejs server setup which runs port 8084. project is having "swagger.json"(which is running on port 80) placed on root path of project under "documentation" directory. Problem is that node server haven't had any code/link that redirects swagger to port 80. how do swagger load proper UI based on json file? If I want to load swagger on different port, how can I achieve the same? swagger version: 2.0