title: How do sessions work in Express.js with Node.js?
body: <p>Using <a href="https://en.wikipedia.org/wiki/Express.js" rel="noreferrer">Express.js</a>, sessions are dead simple. I'm curious how they actually work though.</p>
  
  <p>Does it store some cookie on the client? If so, where can I find that cookie? If required, how do I decode it?</p>
  
  <p>I basically want to be able to see if a user is logged in, even when the user is not actually on the site at the time (like how facebook knows you're logged in when you're on other sites). But I suppose to understand that I should first understand how sessions work.</p>