The original Minecraft client is written in Java. Eaglercraft uses a compiler called to translate Java bytecode into JavaScript.
With the recent turbulence surrounding Eaglercraft repositories and the general confusion surrounding the "Eaglercraft" ecosystem, one of the most common questions in the community right now is simple: modded eaglercraft clients work
Safety is paramount. Always download clients from reputable community hubs or official GitHub repositories. Avoid "leaked" versions of paid clients, as these often contain malicious scripts designed to steal your account tokens or browser cookies. The Legal and Ethical Landscape The original Minecraft client is written in Java