If anyone knows computer science history you probably know that in recent years, programmers now can write backend using Javascript, with NodeJs framework. So, why are we, the newbie programmers, even bother to learn other languages beside Javascript? We are new, we need it to be a little easy, but not so boring. We want to learn exciting things, and Javascript will let us create a complete app from the backend to the frontend. And once we know Javascript very well, converting to other languages isn't as challenge as it would be with other high-level language like Python or Ruby.
So, why spend time on other languages ?
I first learned Python. It's a beautiful language and I love it the most. All the indentations will save the most messy code writers. And then I moved to Ruby. Ruby is quite similar to Python. There are some differences between the two but, well, for learning purpose, they're quite easy to pick up. Perhaps the learning time was quick and I wouldn't say I know everything about Ruby and Python, but I have been learning Javascript for longer than all and still felt like I understand Javascript the least.

Javascript learning path was even worst than Java. Java is a strict language, it requires us to explain everything to it. Without the correct input, Java will not let you code.

Javascript will be really really free, it takes in any type of input, and return any type of data. Sometimes you need to know what it's returning, right? No, it won't let you know unless the definition is right in front of you. Javascript is just "messy" like that.
Also, there are more memes about how weird Javascript is than the rest of the language. What's the difference between NaN, null, undefined, empty array, empty object, oh well...

Java is great for Object Oriented Programming (OOP). You probably wonder what OOP is, I don't know either. I will need to learn in the future.