Very basic ClojureScript Leiningen setup with cljs-devtools

project.clj

(defproject hello-world "0.0.0"
  ;; lein obviously does dependency management
  :dependencies [[org.clojure/clojure "1.8.0"]
                 [org.clojure/clojurescript "1.9.92"]]

  ;; and uses plugins for non-standard tasks
  :plugins [[lein-cljsbuild "1.1.3"]
            [lein-figwheel "0.5.4-4"]]

  ;; this will build cljs on `lein compile`
  :hooks [leiningen.cljsbuild]

  ;; cljsbuild configuraiton
              ;; takes multimple builds (will execute in parallel)
                       ;; choosing a name for a build allows to modify it in other profiles (see below)
  :cljsbuild {:builds {:main {:source-paths ["src"]
                              :compiler {:main hello-world.core
                                         :output-to "resources/public/js/main.js"
                                         :output-dir "resources/public/js"
                                         :asset-path "js"}}}}

  ;; I suggest using profiles from the beginning
             ;; `dev` profile is known to lein and enabled by default
  :profiles {:dev {:dependencies [[binaryage/devtools "0.7.2"]]
                   :cljsbuild {:builds {:main {:figwheel true
                                               :compiler {:optimizations :none
                                                          :source-map true
                                                          ;; namespace to load before the `:main` namespace
                                                          :preloads [devtools.preload]}}}}}
             ;; `prod` key is not known to lein, choose any you want
             :prod {:cljsbuild {:builds {:main {:compiler {:optimizations :advanced
                                                           :pretty-print false}}}}}}

  ;; `resources/public/js` is a non-standard target folder, so we overwrite `clean-targets`
  :clean-targets ^{:protect false} ["target" "resources/public/js"])