The web is already multiplayer

There are no single-player web applications: the simplest model of frontend software is a user interacting with a webpage, but the user and the webpage have similar capabilities. Your frontend application can respond to and produce events. It can modify the webpage.

So can the user: they can modify webpages at any point. Maybe they load every page in a new session, breaking your assumptions about how a website will persist state. Or maybe they never create a new session – they have 80+ tabs open that never get closed, so they will continue using versions of your frontend application that you released months ago, which now break when talking to an updated backend server.

But those aren’t the only players. Browsers are active participants in the game: a browser might translate a webpage and modify the DOM in a way that makes React crash. It might disable an API that the application expects, like localStorage, in a way that makes its behavior unpredictable. Ad-blockers might prevent some of the application from loading.

…

It’s hard work. It’s not cool. And I am nowhere near mastering it. I totally get itwhen people have an aversion to it, or think that the methods used today are wild. But mostly the methods are wild because the problem is, too. A straight-line solution to the problems of the front-end would be lovely, but those problems don’t really permit one.

Source: The web is already multiplayer – macwright.com