Web development is nowadays dominated by many compile to JS languages. ClojureScript is one of such languages. This talk will give overview of ClojureScript language and its ecosystem, and attempts to answer following questions: - Why to use ClojureScript? - Is ClojureScript production ready? - How is the build tooling?

1. ClojureScript for JavaScript
developers
Juho Teperi / Metosin
Webbisauna
1.4.2016

2. Who?
● Juho Teperi / Deraen
○ Mongo, Express, AngularJS, Node.js...
○ Grunt, Gulp
○ 2.5 years Clojure, 1.5 years ClojureScript
○ Open source contributor: Boot & tasks, Cljsjs...
● Metosin
○ Founded 2012
○ Around 11 people
○ World headquarters at Tampere, southern Finland branch at Helsinki
○ Consulting, Software development, Clojure training

3. Contents
● Basics
● Questions / anwers
● ….
● Hot stuff
● Cool stuff
● …..
● ….
● ...

4. Clojure
● A Lisp dialect for JVM
● Functional Programming
○ Immutable data
● Concurrency - STM
● Strongly typed, dynamic typing
○ Static typing as a library
http://clojure.org/about/rationale

5. But Parentheses?
Source: https://xkcd.com/297/

6. Lisp
Allows extending language without changing the
syntax
Compare to ES7

7. ClojureScript
● Clojure dialect
● Compiled to JavaScript
● GitHub statistics
○ 5845 stars, 133 contributors
○ Comparable to other compile
to JS langs

8. Is it useful?

9. Is the compiler slow?
NO
● Not lightning fast, but good enough definitely
○ Improvements recently: fixes, parallel build
○ Room for optimizations
● Incremental compilation

10. Is the resulting code large?
NO
● Google Closure Compiler optimized output (DCE, inlining…)
● The result is small

11. Is the resulting code slow?
NO
● Usually the same
● Immutable data offers benefits sometimes
● http://numergent.com/2015-12/ClojureScript-performance-revisited.html

12. Is it production ready?
YES
● We ported our last AngularJS app to Cljs
● CircleCI (https://circleci.com/blog/)

13. Useful stuff

14. Build tooling
Boot
● Extended using tasks
● Tasks are functions, using
middleware pattern
● Tasks can be composed
Leiningen
● Extended using plugins
● Declarative configuration
● Plugins don’t really compose

15. Dependencies
Yeah, I prefer to NPM.
Also

16. Using JavaScript
First class interoperability
http://cljsfiddle.com/#gist=608eb29293dcc80d9b4145966b53fc49
(js/setTimeout
(fn [] (js/console.log "Hello World"))
1000)

17. Externs
Closure optimizations require extern files

18. How good development experience does
ClojureScript have?
Lets take a look at
https://github.com/Deraen/saapas

19. What was that?
● Boot, boot-cljs, boot-reload etc.
(inspired by Figwheel, a Leiningen plugin)
● Live reload without losing state
● Browser REPL integrated with editor

20. UI programming - Reagent
Global state: http://cljsfiddle.com/#gist=ff59b988ee1760e86ef314acaefd13d1
Local state in closure: http://cljsfiddle.com/#gist=8716f35f9eb042fe963d5ce9b0dca35b
(def beers (atom 0))
(defn beer-counter [{:keys [name]}]
[:div
[:h1 "Hello, " name]
[:p "You have drank " @beers " beers"]
[:button
{:on-click #(swap! beers inc)}
"Drink a beer"]])

21. Common libraries
● Schema, declarative data description and validation
● Core.async, Go style asynchronous programming
● Om, React wrapper
● Om.next, like ^ and Relay style declarative data
requirements
● Reagent, React wrapper with FRP style features
● Re-frame, Redux style architecture model and
implementation for Reagent (great documentation!)
● EDN, extensible data notation (data format)
● Transit, JSON based data format
● Garden, Create CSS from Clojure datastructures

22. Some cool stuff
● ClojureScript-in-ClojureScript: http://clojurescript.net/
● CLJS Fiddle: http://cljsfiddle.com/
● Stand-alone OS X REPL using JSC: https://github.
com/mfikes/planck
● React Native: http://cljsrn.org/

23. Community
● Active Slack community, 5500 members
● Google groups
● /r/clojure
● Multiple conferences in Europe
○ EuroClojure
○ ClojuTRE (announcements coming soon)
○ ClojureX, ClojureD...

24. What is missing?
● Errors are not as great as in Elm
○ Still provides more compile time feedback as JS
■ Missing arguments etc.
● Typing?

25. Thanks!
Questions?

26. Sources & Further Material
● ClojureScript for Skeptics - Derek Slager, ClojureConj 2015: https:
//www.youtube.com/watch?v=gsffg5xxFQI
● ClojureScript: Lisp’s Revenge - David Nolen, GOTO 2014: https://www.
youtube.com/watch?v=MTawgp3SKy8