Standard Minecraft: Java Edition is written in Java and relies heavily on the Lightweight Java Game Library (Lwjgl). Lwjgl provides low-level access to OpenGL, OpenAL, and input devices. Native Java applets are obsolete in modern browsers. To bridge this gap, Eaglercraft utilized , a transpiler that converts Java bytecode into JavaScript and WebAssembly.
Possibly a very stripped-down version via Resentful within 6-12 months, but don't expect smooth 60 FPS on a school laptop.
While some argued that Eaglercraft only allowed access to "offline mode" servers, which do not verify accounts with Mojang's authentication servers, the software itself contained the entire game client. Unlike legitimate "cracked" launchers which require the user to provide their own jar files (sometimes), Eaglercraft often distributed the assets directly to the browser cache. This direct distribution of assets made the 1.20 port a clear target for legal action.