The original game relies on LWJGL for rendering and input. Eaglercraft developers had to write a "wrapper" library that mimics LWJGL calls but translates them into WebGL 2.0 calls. This process effectively tricks the game code into believing it is running on a native desktop environment, while the browser handles the actual rendering pipeline.
Always scan with VirusTotal and use an — never your main Minecraft account.
If you're interested in joining the EagleCraft server, you can usually find the server IP address and connection details on their official website or social media channels.