ATTENTION MOJANG/MICROSOFT EMPLOYEES: THIS REPOSITORY DOES NOT CONTAIN YOUR INTELLECTUAL PROPERTY FILING A FALSE DMCA IS ILLEGAL AND IMMORAL
Eaglercraft uses the decompiled source of the official version of Minecraft 1.8 and 1.12 from Mojang decompiled by MCP http://www.modcoderpack.com/ and compiled to Javascript using TeaVM https://teavm.org/. Therefore it can join any Minecraft 1.12 or 1.8 server, as it is really running (a modified version of) Minecraft 1.12 in the browser. However, due to CORS restrictions it must use a modified version of Bungeecord which proxies the browser's Websocket connection to the pure TCP connection used by Minecraft. For graphics, a custom compatibility layer created by me allows the fixed function OpenGL 1.3 based rendering engine mojang uses to operate through an HTML5 WebGL canvas with minimal changes to the source.