What is it

Hosted language

A language that targets different platforms

Hosted language

Clojure   ☛   JVM

ClojureScript   ☛   JavaScript

JavaScript Runtimes:

Browsers

Node.js

About the Language

Lisp family

(((((())((((((()))))()()(((())))))))

Functional programming language

• Immutability by default
• First class functions
  
• Programming with values
• Declarative-ish (map, filter, etc)
  

A practical language

• Not pure fp
  
• Really easy to interop
• You can step out of the defaults
  when necessary
  

Differences from others

How is it different from coffeescript, typescript, ...?

Changes some JavaScript semantics (to be saner)

• Equality (values)
  
• Falsy/Truthy
  
• Sane scoping (-hoisting)

Provides a consistent full language and ecosystem

• Modules
• Package management
• Great standard lib
• Good practices and philosophy

Cool stuff in clojurescript

Values FTW

Immutable by default

Cool stuff in clojurescript

Concise and expressive

Cool stuff in clojurescript

To the code!

Super basics

Setup

• Lighttable
  
• Git
• Leiningen

Small intro to Lighttable

Code Samples

github.com/joakin/diving-into-clojurescript-exercises

 
  git clone git@github.com:joakin/diving-into-clojurescript-exercises.git

Connect to Lighttable UI

Code samples are in basic/

Prerequisites 01-pre.cljs

Exercise 01.cljs

Solutions are in 01-sol.cljs

Reference

Basic syntax

himera.herokuapp.com

Synonyms

clojure.core

http://clojure.github.io/clojure/clojure.core-api.html
http://clojuredocs.org/clojure_core/1.3.0/clojure.core

Interactive TUTORIAL

swannodette/lt-cljs-tutorial

   git clone git@github.com:swannodette/lt-cljs-tutorial.git 

Getting the hang

4clojure.com

Do it yourself

Check the docs

Look at the community results (Follow top members)

Lets make some apps

The artsy wall

We are going to walk through the creation of a canvas fullscreen app

A wall of colorful squares that vibrate

joakin/diving-into-clojurescript-exercises/futurejs-wall

Steps are stored in src-steps (see README)

Interesting things to learn

• Live coding
• Namespaces
• Including external libraries
• Source maps
• JS interop
  

LT plugins web app

We are going to make a web app that will consume a service

via ajax and will render the contents.

joakin/diving-into-clojurescript-exercises/lt-plugins

Steps are in the README

Project management

Leiningen

• Create new projects (templates)
  
• Fetch dependencies for your project
• Run tests
• Run a fully-configured REPL
• Compile sources
• Run the project
• Compile and package projects for deployment
• Publish libraries to repositories such as Clojars
• Automation tasks (leiningen plug-ins)

  lein help tutorial | less

Creating New projects

lein help new

Clojurescript templates

lein new mies awebsite

How do I compile ClojureScript?

cljsbuild

Leiningen plugin for compiling ClojureScript

In project.clj  ☞

  :plugins [[lein-cljsbuild "1.0.2"]] 

Sample conf:

  :cljsbuild {
    :builds [{:id "awebsite"
              :source-paths ["src"]
              :compiler {
                :output-to "awebsite.js"
                :output-dir "out"
                :optimizations :none
                :source-map true}}]})

lein cljsbuild once awebsite # just build once

lein cljsbuild auto awebsite # watches changes and recompiles incrementally 

Development workflow

1. Launch compiler watch
2. Open project in LightTable
3. Open browser tab with index.html
4. Live eval!
5. Docs
6. Autocomplete
7. Watches
   

Compilation modes

Clojurescript compiler features several compilation modes

project.clj with all the options commented

Each mode has different tradeoffs:

• Development speed
• Multiple files vs 1 file
• Code minification
• Code optimizations

 Clojurescript compiler  ☞  cljs ► standard library & js

Google closure compiler  ☞ merging files, minification, optimizations

Optimizations: none

• No optimizations
• Lots of files
• Fastest compilation (& incremental)
• Dev oriented
• Specific imports in html

  :cljsbuild {
    :builds [{:id "awebsite"
              :source-paths ["src"]
              :compiler {
                :output-to "awebsite.js"
                :output-dir "out"
                :optimizations :none
                :pretty-print true
                :source-map true}}]}

        <script src="out/goog/base.js" type="text/javascript"></script>
        <script src="awebsite.js" type="text/javascript"></script>
        <script type="text/javascript">goog.require("awebsite.core");</script>

Optimizations: Whitespace

• Cleans whitespace and comments
  
• One file
  
• "Fast" compilation (less than none)
• Readable JS
  

  :cljsbuild {
    :builds [{:id "awebsite"
              :source-paths ["src"]
              :compiler {
                :output-to "awebsite.js"
                :output-dir "out"
                :optimizations :whitespace
                :pretty-print true
                :source-map true}}]}

        <script src="awebsite.js" type="text/javascript"></script>

Optimizations: SIMPLE

• One file with simple optimizations
  
• Slower compilation
• One import in the html
  

  :cljsbuild {
    :builds [{:id "awebsite"
              :source-paths ["src"]
              :compiler {
:output-to "awebsite.js" ; No output-dir (only the file)
                :optimizations :simple
                :pretty-print true
                :source-map "awebsite.js.map"}}]} ; Sourcemaps are a file now, not true

        <script src="awebsite.js" type="text/javascript"></script>

Optimizations: ADVANCED

• One file (smallest size)
  
• Slowest compilation
• One import in the html
• Agressive optimizations, minification and code rewrites
• Performance  and size gains
  

  :cljsbuild {
    :builds [{:id "awebsite"
              :source-paths ["src"]
              :compiler {
:output-to "awebsite.js"
                :optimizations :advanced}}]}

        <script src="awebsite.js" type="text/javascript"></script>

Notes

Options pretty-print and source-maps are optional.

They increase compilation time.

(Incrementally not so much)

Suggestions

Use :optimizations :none with :pretty-print true and :source-maps true

for development workflows (using lein cljsbuild auto (pure delight))

Use :optimizations :advanced for staging and production.

(Staging with :source-maps and :pretty-print, production without).

Some informal benchmarks

lein cljsbuild once

 Successfully compiled "awebsite.js" in 9.214 seconds.

 Successfully compiled "awebsite-w.js" in 14.045 seconds.

 Successfully compiled "awebsite-s.js" in 19.269 seconds.

 Successfully compiled "awebsite-p.js" in 18.701 seconds.

lein cljsbuild auto

 Successfully compiled "awebsite.js" in 0.05 seconds.

 Successfully compiled "awebsite-w.js" in 4.126 seconds.

 Successfully compiled "awebsite-s.js" in 5.918 seconds.

 Successfully compiled "awebsite-p.js" in 4.188 seconds. 

Some informal sizes

Libraries

We can distinguish 3 kinds of libraries that we can use

(and require different treatment)

1. ClojureScript libraries
2. Google Closure compatible libraries
3. Other libraries from the JS ecosystem
   

Clojurescript libraries

Hosted in lein compatible repos (clojars)

How to find them:

Github search

Clojars

Google groups

Or Google

Just include them in your project.clj and go:

  :dependencies [[org.clojure/clojure "1.5.1"]
                 [org.clojure/clojurescript "0.0-2173"]
                 [rm-hull/monet "0.1.11"]] 

Restart the compiler so that it downloads it

Google Closure

Big set of cross browser libraries written by Google

API

Example:

API, importing & real_world_usage

Lots of interesting stuff: Format, Color, Events, Dom, Style, ...

Takes advantage of Advanced compilation

(deletes code you don't use and inlines code where it can)

Google Closure

The compiler has and includes as necessary a version of the closure libs

You can specify a specific version of the google closure libraries:

  :dependencies [[org.clojure/clojure "1.5.1"]
                 [com.google.javascript/closure-compiler "v20131014"]
                 [org.clojure/clojurescript "0.0-2173"
                  :exclusions [com.google.javascript/closure-compiler]]

Google closure compatible libs

Libraries written with the closure compiler optimizations in mind.

Not a whole lot of them.

They take advantage of code optimizations and compiler errors (docs)

Example (Download react to your project):

  :compiler {
    ; ... rest of arguments
    :foreign-libs [{:file "reactjs/react.js"
                    :provides ["React"]}]
    :externs ["reactjs/externs/react.js"]} 

Other libraries

Almost all of the JS libs.

Include the code in your project,

If it has externs, you include them:

          :preamble ["react/react_with_addons.min.js"
                     "gifjs/dist/gif.js"] ; or link them in the html

          :externs ["react/react_with_addons.js"
                    "gifjs/dist/gif.js"]

1. Include the library as its own externs
2. Try to autogenerate them with lein-externs
3. Write a dummy externs-whatever.js 

Other libraries

Pros:

HUGE ecosystem

Lots of good libraries

(moment.js, react.js, hammer.js, bluebird, async, d3.js, bacon.js, ...)

Cons:

No optimizations or unused code removal

Bigger size of bundle because of libraries

We have to take care of externs with advanced

Suggestion:

If there is a good cljs lib, use that. Otherwise, go wild.

Some Cool cljs libraries

...

Testing

Live development is no substitute for tests

Several options:

clojurescript.test

clojurescript.test

Full complete test library (port of the clojure version)

Well mantained and documented

To use it just add it to your plugins in project.clj

    :plugins [[com.cemerick/clojurescript.test "0.3.0"]]

• Run tests from the repl
  
• Run tests each time cljsbuild compiles

:cljsbuild {:builds [ ... ]
            :test-commands {"unit-tests" ["phantomjs" :runner
                                          "this.literal_js_was_evaluated=true"
                                          "target/cljs/testable.js"
                                          "test/cemerick/cljs/test/extra_test_command_file.js"]}}

:test-commands {"unit-tests" ["node" :node-runner
                              ; extra code/files here...
                             ]}

clojurescript.test

Simple and easy to understand

  (deftest somewhat-less-wat
    (is (= true (some-function "whatever"))))

Both sync and async support

(deftest ^:async timeout
  (let [now #(.getTime (js/Date.))
        t (now)]
    (js/setTimeout
      (fn []
        (is (>= (now) (+ t 2000)))
        (done))
      2000)))

specljs

BDD style testing (specs)

  :dependencies [[org.clojure/clojure "1.5.1"]]
  :profiles {:dev {:dependencies [[speclj "3.0.0"]]}}
  :plugins [[speclj "3.0.0"]]
  :test-paths ["spec"]

:cljsbuild {:builds        {:dev  {:source-paths ["src/cljs" "spec/cljs"]
                                   :compiler     {:output-to "path/to/compiled.js"}
                                   :notify-command ["bin/speclj" "path/to/compiled.js"]}
            :test-commands {"test" ["bin/speclj" "path/to/compiled.js"]}}

(ns sample.core-spec
  (:require-macros [speclj.core :refer [describe it should should-not run-specs])
  (:require [speclj.core]
            [sample.core :as my-core]))

(describe "Truth"

  (it "is true"
    (should true))

  (it "is not false"
    (should-not false)))

(run-specs)

Purnam

Jasmine based testing (used with Karma)

  :dependencies [[im.chit/purnam "0.4.3"]]

(describe "Addition"
    (it "should add things"
      (is (+ 1 1) 2)))
      

Others

There are more, and also wrappers for JS libraries.

You could ignore all this and just use a JS library for testing (interop)

(Why?)

Property-based testing

Instead of enumerating expected input and output for unit tests,
you write properties about your function that should hold true for all inputs.

Double-check

(def sort-idempotent-prop
  (prop/for-all [v (gen/vector gen/int)]
    (= (sort v) (sort (sort v)))))

(tc/quick-check 100 sort-idempotent-prop)

(defspec first-element-is-min-after-sorting ;; the name of the test
         100 ;; the number of iterations for test.check to test
         (prop/for-all [v (such-that not-empty (gen/vector gen/int))]
           (= (apply min v)
              (first (sorted v)))))

Macros

Code generating/rewritting code that gets run at compile time.

(Code is data, as you have seen)

ClojureScript macros are written in clojure (.clj files)

Reading, evaluation and macros

Writing macros

Super powerful, useful, language is infinitely extensible by users

Complicated to debug, best avoided unless necessary (maybe)

Examples

(defmacro when
  "Evaluates test. If logical true, evaluates body in an implicit do."
  {:added "1.0"}
  [test & body]
  (list 'if test (cons 'do body)))

(macroexpand '(when (the-cows-come :home)
                (call me :pappy)
                (slap me :silly)))
; =>
(if (the-cows-come :home)
  (do (call me :pappy)
      (slap me :silly)))

(defmacro unless
  "Inverted 'if'"
  [test & branches]
  (conj (reverse branches) test 'if))

(macroexpand '(unless (done-been slapped? me)
                      (slap me :silly)
                      (say "I reckon that'll learn me")))
; =>
(if (done-been slapped? me)
  (say "I reckon that'll learn me")
  (slap me :silly))

So...

They are a tough topic, and great books and articles are available.

Look for Clojure macros, not ClojureScript specifically

Super powerful, enable users to extend the language via libraries

in ways inconceivable in other languages (JS? Damn ECMA)

We will see the power in the next section.

Some uses:

Rewrite code (unless, core.async)

New syntax constructs

Optimize code (compile time) (dommy)

Sweet JS

Mozilla leaded effort to have macros in JavaScript

Opt-in macros

More verbose because syntax (code is not data),

but brings the power and responsibility to JS

Example: ES6 syntax, Ki (lisp+mori)

superpowers

Great philosophy, vision, community and people

with a great language produce awesome powerful things

core.async

Go style concurrency (CSP) implemented as a library!

Turns syncronous looking code into CPS (callbacks)

Concurrent code in single threaded JS!

(defn init []
  (let [clicks (listen (dom/getElement "search") "click")
        results-view (dom/getElement "results")]
    (go (while true
          (<! clicks)
          (let [[_ results] (<! (jsonp (query-url (user-query))))]
            (set! (.-innerHTML results-view) (render-query results)))))))

  (defn get-user [id]
    (let [out (chan)]
      (db-query-user {:id id} (fn [user] (put! out user)))))

  (defn update-user [user]
    (db-update-user user (fn [err] (put! out err))))

  (def handler [req res]
    (go
      (let [user (<! get-user (.id req))
            result (<! update-user user)]
        (.send res (if (nil? result) "OK" "BROKE"))))

Core.async

(let [c1 (chan)
      c2 (chan)]
  (go (while true
        (let [[v ch] (alts! [c1 c2])]
          (println "Read" v "from" ch))))
  (go (>! c1 "hi"))
  (go (>! c2 "there")))

(go (try
      (let [tweets    (<? (get-tweets-for "swannodette"))
            first-url (<? (expand-url (first (parse-urls tweets))))
            response  (<? (http-get first-url))]
        (. js/console (log "Most recent link text:" response)))
      (catch js/Error e
        (. js/console (error "Error with the twitterverse:" e)))))

Core.match

An optimized pattern match and predicate dispatch library for Clojure.

(doseq [n (range 1 101)]
  (println
    (match [(mod n 3) (mod n 5)]
      [0 0] "FizzBuzz"
      [0 _] "Fizz"
      [_ 0] "Buzz"
      :else n)))

(let [x 1 y 2]
  (match [x y]
    [1 b] b
    [a 2] a
   :else nil))

(let [x {:a 1 :b 1}]
  (match [x]
    [{:a _ :b 2}] :a0
    [{:a 1 :b 1}] :a1
    [{:c 3 :d _ :e 4}] :a2
    :else nil))

(let [x [1 2 3]]
  (match [x]
    [[_ _ 2]] :a0
    [[1 1 3]] :a1
    [[1 2 3]] :a2
    :else :a3))

core.logic

Prolog-like relational programming, constraint logic programming,

and nominal logic programming for Clojure

(run* [q]
  (== q true))
;;=> (true)

(run* [q]
  (membero q [1 2 3])
  (membero q [2 3 4]))
;;=> (2 3)

 (run* [q]
   (== {:a q :b 2} {:a 1 :b 2}))
;;=> (1)

(run* [q]
   (fresh [a]
     (membero q [1 2 3])
     (membero a [3 4 5])
     (== q a)))
;;=> (3)

core.typed

Gradual typing in Clojure, as a library.

  (ann ^:no-check foo (Fn [Number -> Number]))
  (defn foo [a]
  'a)

  (ann bar [Number -> Number])
  (defn bar [b]
    (+ 2 (foo b)))

closeup

Learn new things that suppose significant brain effort

Bring what you learned to your daily work (at least the concepts)

Embrace immutability (eases reasoning about code)

Play and have fun

Where to get help

StackOverflow

Google Groups

irc #clojurescript on freenode.net