I think you are confused on what exactly a MUD is. A MUD has
nothing to do with web development, so in turn, it has
nothing to do with Javascript, HTML 4 or 5, PHP, etc. MUDs are typically written in either C or C++, although a handful are written in Java (not Javascript) and C#. They are not accessed in the same way websites are. Instead, users connect with a "Telnet" client, which just simulates a text-based terminal. The server for a MUD does not run on a web server. Really, MUDs are closer in development and use to a real MMORPG server, like the servers to World of Warcraft, than they are to a web game. Some MUDs can be played in a web browser, but that is an illusion, as they have used something like Java or Flash to write a real Telnet client that runs in the browser. They are not browser-based games.
"Diku" was an old MUD codebase that I believe was written in C in 1990. Thus, it is older than the internet. The word "Diku" only means one, specific MUD codebase. What differentiated it from other MUDs was its heavy focus on killing mobs, leveling up, gaining better equipment, etc. (basically like almost every MMORPG out today, which all borrow heavily from Diku). Other MMOs and MUDs can be called "Diku-like", but they are
not Diku, since Diku is technically neither open source, nor free software (although it somewhat resembles both).
For the time being, if you want to develop an actual MUD, you must do traditional server programming, using sockets, and other fairly complex programming tasks, and it will most likely either be in C, C++, Java, C#, VB.NET, etc. While Javascript may have a passing resemblance to Java and shares part of the same name, they are completely unrelated. A MUD has nothing to do with HTML, Javascript, PHP, or other web programming languages. If you want to develop a browser-based RPG, like
Legends of Zork, you will find that most of this forum is dedicated to that, since the admin and owner, Hallsofvallhalla, has made a lengthy video tutorial about their creation. Thus, much of the community here has gathered with that common interest. I think I am one of the few people here with some knowledge and interest in regards to MUD development, though. They really are a dying breed, with only Iron Realms and Simutronics games enjoying any continued commercial success.