Monday, January 11, 2021

Simple (within parentheses)

  • - Hey, what's ClojureScript?
  • - It's a thing that compiles Clojure to JavaScript.
  • - I get it. What's Clojure?
  • - It's a Lisp.
  • - ???
  • - You know, a functional programming language that uses a lot of parentheses.
  • - I … get it? 🤯

Don't worry. In this post, I will share some of the basics that I have learned about Clojure and ClojureScript.


With Clojure, you can write simple, functional and minimalistic code. Some of the cool things with Clojure are:

  • data is immutable
  • the REPL is a powerful tool
  • few keystrokes to make things happen

Clojure runs on top of Java, suitable for all kinds of "backend" things. It also runs on top of JavaScript. Yes, JavaScript - making it possible to develop all kinds of apps, tools, products and websites. There's even an option to run in a .NET runtime, but I haven’t tried out that one yet.

What does it look like?

Even though the syntax may look unfamiliar, you can already see in this silly example the less amount of keystrokes needed using Clojure, compared to JavaScript.


Everything you write in Clojure is a list, wrapped in parentheses. That may sound weird. I agree, it is weird. But your eyes will get used to it. In short, the format of writing something in Clojure is:

(operator operands) or even (function arguments)

Here is an example:

... and how it would be written in JavaScript:

If all this is new to you, you might have this expression in your face right now: 😬

That is perfectly normal. I have looked like that a lot during 2020. When digging deeper, you may need to go through The 12 Stages of Learning Clojure.


With ClojureScript, you develop web apps and write simple React components. You write code in Clojure, compile it to native JavaScript and run it in your favorite browser. The compilation happens all the time and automagically as you type.

Just like with Java or .NET in the backend, ClojureScript has native access to JavaScript. You can use and interact with your favorite npm packages and React components just as you would with JavaScript.

Reagent and React

I'm going to fast-forward a bit by adding a ClojureScript library called Reagent. With Reagent, you write React components but with Hiccup instead of JSX. Wait, what?

View components are built up using Clojure data structures. The example above creates html elements with Clojure vectors and keywords. This style is called Hiccup. It will save you a lot of keystrokes and you'll have a lot less of scrolling in your code editor.

What about state?

I'll fast-forward again by adding a very nice library called re-frame.

From the re-frame docs:
“... It has reactivity, unidirectional data flow, pristinely pure functions, interceptors, coeffects, conveyor belts, algebraic effects, statechart-friendliness and claims an immaculate hammock conception. All while being both simple and easy. ...” 💥🤯💥

With re-frame, data is stored in one place called the "app db". Your components will fire events and subscribe to changes in the app db. The cool thing is that you write code in a sequential way, making it very readable and easy to understand. However, the syntax of the actual events and subscriptions might take a while to understand, at least if you are new to Clojure in general.

Here, we have a Reagent component that adds a button component, only when the app is disconnected. It is subscribing to changes of disconnected in the app db. React will re-render the components when the app state has changed.

Cool, but can I use my favorite editor?

Yes, most likely. I know there are Clojure plugins for VS Code, Atom, Sublime Text and intelliJ. I use Emacs, because ... I just like it.

There is something important and special going on with developers and their text editors. I think you will be able to find your favorite dev setup. I also think that you will learn a lot of new programming concepts and styles when reading more about this cool language and its libraries.

Photo by Marcos Paulo Prado on Unsplash