I suspect Java applets fell out of fashion because they could only manipulate a rectangular area of the screen and not the DOM. Did the DOM even exist in 1995?
So in the end it was security nightmare.
Jobs finally killed it, by declining to support Java on iPhones. So from that point it was doomed.
WASM is part of the browser. Browser vendors figured out how to keep their browsers evergreen. You don't need to install anything, it just works. It works on iPhones.
So, yes, idea was the same, but implementation was actually good and supported by everyone.
It's also not the fact that users rejected the idea of apps that are restricted to a rectangle inside the web browser - after all, Flash and even ActiveX (to a limited degree) managed to churn out popular apps running inside a (badly) sandboxed rectangle. Some of the popular use cases (e.g. games) did not die, and are now faithfully served by WASM. Rectangle-constrained applets are obviously not good for every use case, but Java applets failed to succeed even at the places where Flash shined later.
Looking back, I think what killed Java applets was that they were just slow, ugly, hard to interact with and had bad developer experience. Developing HTML pages was easy - just a change/reload cycle. The same goes for cgi-bin scripts. Java applets required compilation, packaging and then testing, at the time when automated building tools were not there. IDEs with RAD designers that tried to improve the experience did come, but at least most Java IDEs I tried back then were quite cumbersome to use compared to incumbent native RAD tools like Delphi or Visual Basic.
In addition to that, Java applet support was initially spotty during the browser wars, and features such as JAR files and different JDK 1.1 (and later JDK 1.2) APIs were not evenly supported across Netscape Navigator and Internet Explorer[1]: https://www.infoworld.com/article/2076251/applets--still-ess...
And then there's the slowness and ugliness. You really only had AWT available for your UI and graphics, and it sucked. It was ugly, buggy and slow. In theory, it shouldn't have been so, but the technology just wasn't ready and just wasn't mature enough.
I think Flash was so wildly successful because it took an entirely different (and less ambitious) route at the beginning. Flash started as a multimedia player with user-friendly authoring tools. They later added ActionScript and Flash itself become the RAD tool that could penetrate the web frontend.
I remember just sitting around looking at these Java Applets loading whole applications. While Flash games were snappy.
The moment you hit some webpage and it shows you a Java Applet loading bar you knew the website was useless basically.
I think this had quite a bit to with Java and the way it implemented UIs. Also just serving a whole bunch of unnecessary stuff. To be fair this eventually became an issue with JS as well, but not the the same degree compared to the network speed.
Flash loaded quickly and seamlessly, but otherwise had all the same problems.
Some info about the LAYER API (which Netscape eventually killed, as the MS/W3C DOM prevailed):
http://web.archive.org/web/19971015223701/http://developer.n...
Also, a DOM compatibility guide can be found here:
Remember that even after JS was released it still took many years until it became fast enough to use for big applications. If I'm not wrong, Google Chrome was made partly with the explicit goal to have super fast JS.
Also no the DOM did not exist until 1998.
While the limited facilities provided in the first generation of JavaScript and JScript for detecting events and manipulating HTML elements eventually came to be known as "DOM Level 0", it wasn't until 1998 that the first DOM specification was published. Source: https://en.wikipedia.org/wiki/Document_Object_Model