Web-based page session

I'd like to create a web app where the user is able to create a session, with the session being accessible even after leaving the page/browser.

An example would be http://lichess.org where the user goes to 'Create a game' and a page is created. That page then remains accessible even after the session is finished; see: http://ift.tt/1CnCUV6

Essentially what I'd like to know is, what would be needed in order to create a similar effect. I've programmed tonnes over the years, just web environments are new to me! Scala seems like a contender, but in all honesty I have no clue. Perhaps javascript?

Any advice would be appreciated, thanks.