Today, the web isn’t what you remember.
It used to be stateless. Every call to your site began with a detective story of figuring out who the user was and hydrating their “state” so you
could continue useful work. The web didn’t remember state.
It used to be based on request and response. Code was delivered to the browser like a postman dropping off a package and speeding away. You had to call back in to get updates. Sure, we have AJAX to poll for updates these days, but those are just endless calls for new packages behind the scenes. The web wasn’t realtime.
It used to be filled with static applications. Users click on the buttons, controls, and widgets provided and the web application can only do
what the developer implemented. Sure, we “extend” web sites with REST “APIs”, but this isn’t the same thing as an SDK.
Start building extensible and powerful web applications after seeing how the way the web works is changing for good.