That is absolutely not the case. There's a huge difference between having immutable constructs available in a language and immutability being the default. Cloj

That is absolutely not the case. There's a huge difference between having immutable constructs available in a language and immutability being the default. Clojure is built around the idea of immutability from ground up. It makes it natural to work with immutable data, and it guides you towards doing the right thing. An example of this would be transients, which allow you to do local mutation within a function, but the compiler will give you an error if you try to leak mutable state. All of this greatly reduces mental overhead for the developer because vast majority of code is referentially transparent. You can reason about functions in isolation without having to know anything about the rest of the application. Meanwhile, simply bolting on immutable constructs on top of JavaScript puts the burden of using them correctly squarely on the developer. It's still perfectly possible to stick a mutable reference into your immutable record, and then pass it around and modify it. The language does nothing to help you there. Furthermore, you have to consider the culture and the ecosystem around the language. Pretty much all Js libraries are written in imperative style, and passing mutable data is the accepted practice. And immutability is just one aspect, there are plenty of other differences that are very important for many daily tasks. One major difference is that Clojure is a much smaller and consistent language. Clojure code tends to follow a few accepted patterns that the community settled on. Js is a giant language that's grown organically and acquired tons of quirks and gotchas over the years. It's a minefield compared to Clojure. Another day to day benefit of using Clojure is its tooling. You get reliable hot loading, which is pretty much impossible with Js, you have sane library management, minification, code pruning to function level, and code splitting out of the box. These features are especially important when shipping code across the network to the browser. You also get a REPL where you can connect your editor to your running application, and interact with it directly from there. Any time you write a function, you're able to run it immediately and see what it does. There's no waiting for your code to compile, or the page to reload, or having to rebuild the state. It's an incredibly tight feedback loop. In short, there's no comparison between ClojureScript and Js regardless of what constructs get bolted onto Js in the future.