Well you're right that people can turn JavaScript off, but these days most people don't. Without getting too deep into the technical stuff, JavaScript is what makes dynamic web pages and web apps possible. If a page's content changes without the entire page reloading, more often than not they used JavaScript to do it. And on the off-chance someone has JavaScript turned off, you can use the <noscript> tag to show a message letting people know they need to turn it on to play the game.
Oh, and one other thing, in case you didn't know: JavaScript is not the same thing as Java. Java is a general-purpose programming language, used for a lot of different stuff (the biggest one being Android apps). It's still used on the web, but I don't recommend it. JavaScript on the other hand is the main language of the web. No matter what else is used (PHP, Java etc. or none in your case) a web page can't do much without JavaScript.