There's a world where browser UIs are programmed in Smalltalk instead, which I think is what the authors of the DOM may have intended when building it out OOP-style.
It would bear almost no resemblance to the web we have today, but message passing between UI components throughout various parts of their lifecycle has been a great way to model an interface for decades. You only need to look at the overall fit and finish of a typical MacOS or iOS app, with Swift simply pulling Objective-C into the 21st century.
Web UIs tend to make heavy use of message passing via event listeners.
The major difference between web UIs and desktop apps is two fold.
In web UIs, you don’t generally have an event loop in which you change your app state based on system input events and there is, generally, a slow request/response cycle for any interaction.
That’s why immediate mode UI doesn’t really fit well in web land.
It would bear almost no resemblance to the web we have today, but message passing between UI components throughout various parts of their lifecycle has been a great way to model an interface for decades. You only need to look at the overall fit and finish of a typical MacOS or iOS app, with Swift simply pulling Objective-C into the 21st century.