JavaScript vs Closure - What's the Difference?

In your book er, you showd how to implement certain things that are available in a language like close or hasca rit. You should probably not implement all of that from scratch, but use a library for it. There are different libraries, and inthe jarvascript ecosystem, where like people who use immutable j s and and libraries like that. What do you think people missing that are using javascript, using oneo or two function libraries, in comparison to using a language like closure? Like, what do they gain if they really move to a functional language?