I am building a WebApp (ERP) and I need to display the people currently logged in and active on the page. I managed to get something pretty accurate by listening on the mouse/keyboard events and periodically reporting to the DB.
I don't know how to mark people offline when they close the page. I tried using onbeforeunload, but it obviously fires when the user simply changes pages (click a link inside the ERP, that point to another page in the ERP).
I then tried to use WebSockets, but the problem is the same : everytime the page is realoded, the WebSockets connection is closed.
So I can think of two ways:
Use WebSockets indeed, and replace all links by a call to a javascript function that would somehow tell the server that the user is going to change page (so that the server doesn't mark it as offline). But that doesn't feel right, semantically speaking, links should be links, it simply points to another location.
Use either WebSockets or AJAX and never actually change page: links are replaces by a function that will call for the content, and display it on screen (updating the DOM with Javascript). But again, it doesn't feel right either, because semantically speaking the page would have no meaning and the URL would never change, so the user can't "copy paste" the link of the page to refer to it, right?
So, is there a proper, clean way of doing this?
If each of your pages has a webSocket connection to your server, then on the server you can see when any given page is closed by seeing that the webSocket gets closed.
To avoid thinking that a user has left the site when they are just navigating from one page in your site to another, you simply need to add a delay server-side so that you only report that the user has left your site if there has been no webSocket connection from this user for some time period (probably at least a few seconds).
So, on your server when you detect that the last webSocket connection for this user has been closed, you set a timer for some number of seconds. If the user opens up another page on your site (either via navigation or just opens another page) before the timer goes off, you cancel the timer and count the user as still connected. If the timer goes off, then you now know that the user has been away from your site for whatever time period you picked (say 10 seconds) and to you, this will signify that they have left the site. You can control how long you want that time period to be before you decide that, yes they are gone.
All attempts at trying to "see" the user leaving your page IN the browser with Javascript are going to have holes in them because there are always ways for a web page to get closed without your client-side javascript having a chance to tell your server. The beauty of the webSocket solution is that the browser automatically and reliably tells your server when the page is now gone because it closes the webSocket and your server receives the notification that the socket has been closed.