Learning a new programming language can be hard. However, learning idiomatic JavaScript is not if you're already a Clojure developer. In fact, this statement could be extended to say that JavaScript will be rather easy to pick up for many developers that are knowledgeable in a functional programming language.

Generally speaking, functional programming can be boiled down to the idiom that you write your programs through intense usage of a few versatile data structures and many composable functions. Clojure is such a language. JavaScript initially was created with Scheme and Self in mind, therefore it supports both the paradigms of functional programming and object orientation. Modern JavaScript has lots of syntax on top of a very lean and arguably beautiful core. However, the additional syntax absolutely isn't required to write well structured idiomatic JavaScript code. In fact, it is an ongoing debate on whether or not it generally is a good idea to blow the language spec up as much as it did in the last years. The additional syntax can help you where it makes sense, but there's no need to start learning all that and a functional core take you very far! Therefore, if you know a LISP, you're already halfway done to becoming a good JavaScript developer! If you also know a language with a "standard" class-based hierarchy approach (Ruby, Python, Java, C#, you name it), you're even closer to writing great JavaScript code!

Clojure and JavaScript share many attributes which you don't have to re-learn:

  • Dynamic Typing
  • Employs similar types
  • Functional Programming (first class functions, anonymous functions, closures)
  • Garbage Collection

To quickly transpose your development knowledge, you have to ask the following questions:

  1. What data structures should I use?
  2. Where do I get my functional vocabulary?
  3. How do I structure my code?
  4. What's different in JavaScript?

1 Data Structures

I'll make a stretch and say that Maps and Vectors are the most important data structures in Clojure (at least to get started). JavaScript has two data structures which are similar to those. Of course they are not persisting, so they are not exactly the same. However the other attributes are very similar.

Maps are Objects

https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects

Vectors are Arrays

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

2 Functional Vocabulary

3 Code structure

  • Small applications can easily be built in one file by just writing functions, same as in Clojure: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions
  • If in Clojure, you'd like to introduce a new Namespace, go for a module in JavaScript: https://hacks.mozilla.org/2018/03/es-modules-a-cartoon-deep-dive/
  • If you need further abstraction, you can introduce a class: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes
  • For packaging your application (making it available) and importing other libraries, use NPM

4 What is different/special in JavaScript?

Concurrency and Event Orientation:

Many things make JavaScript special, but one of the most interesting properties is that doing I/O is never blocking! JavaScript is heavily event oriented. Handling I/O is performed via events and callbacks/promises.

Example:

setTimeout(function() {
  console.log("This text appers in 2s as a log message.")
}, 2000)

Read more about the concurrency model and event orientation here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop

Biggest OSS community

There are currently over 700'000 packages on NPM with about 40% year over year growth.

Of course, quantity and quality are not the same. There's lot's of churn and the 'new hotness' sometimes is quickly replaced by 'the leading edge'. However, a benefit of writing idiomatic functional code is that your code will persevere!

Great documentation

Learn how to program in JavaScript with equally good high-level guides and in-depth tutorials: https://developer.mozilla.org/en-US/docs/Web/JavaScript