deps.edn

{:deps {org.clojure/clojurescript {:mvn/version "1.10.520"}
        lilactown/hx {:local/root "../../opensource/hx"}
        
        com.bhauman/figwheel-main {:mvn/version "0.2.0"}
        com.bhauman/rebel-readline-cljs {:mvn/version "0.1.4"}}
 :paths ["src" "resources" "target"]
 :aliases {:build {:main-opts ["--main" "cljs.main"
                               "--compile-opts" "prod.cljs.edn"
                               "--compile"]}
           :dev {:main-opts ["--main" "figwheel.main"
                             "--build" "dev"
                             "--repl"]}
           :lint {:main-opts ["./bin/lint.clj" "./src" "./test"]
                  :extra-deps {lein-bikeshed {:mvn/version "0.5.1"}
                               jonase/kibit {:mvn/version "0.1.6"}
                               clojure-term-colors {:mvn/version "0.1.0"}}}
           :test {:extra-paths ["test"]
                  :extra-deps {olical/cljs-test-runner {:mvn/version "3.5.0"}}
                  :main-opts ["-m" "cljs-test-runner.main"]}}}

dev.cljs.edn

^{:open-file-command "emacs"
  :ring-handler clj.server/handler
  :ring-server-options {:port 3449}
  :extra-main-files {:devcards {:main demo.devcards}}
  :watch-dirs ["src"]}
{:main demo.core
 :devcards true
 :npm-deps false
 :closure-defines {demo.constants/environment "development"
                   goog.DEBUG true}
 :externs ["src/js/externs/react/react.ext.js"
           "src/js/externs/react/react-transition-group.ext.js"
           "src/js/externs/jss/jss.ext.js"]
 :foreign-libs [{:file "dist/index.bundle.js"
                 :provides ["jss"
                            "jss-preset-default"
                            "react"
                            "react-dom"
                            "react-transition-group"]
                 :global-exports {jss jss
                                  jss-preset-default jssPresetDefault
                                  react React
                                  react-dom ReactDOM
                                  react-transition-group ReactTransitionGroup}}]}

index.js

import jss from 'jss';
import jssPresetDefault from 'jss-preset-default';
import React from 'react';
import ReactDOM from 'react-dom';
import * as ReactTransitionGroup from 'react-transition-group';

window.jss = jss;
window.jssPresetDefault = jssPresetDefault;
window.React = React;
window.ReactDOM = ReactDOM;
window.ReactTransitionGroup = ReactTransitionGroup;

prod.cljs.edn

{:main demo.core
 :output-dir "target/public/cljs-out"
 :output-to "target/public/cljs-out/prod-main.js"
 :npm-deps false
 :infer-externs false
 :optimizations :advanced
 :closure-defines {demo.constants/environment "production"}
 :pseudo-names true
 :pretty-print true
 :verbose true
 :externs ["src/js/externs/react/react.ext.js"
           "src/js/externs/react/react-transition-group.ext.js"
           "src/js/externs/jss/jss.ext.js"]
 :foreign-libs [{:file "dist/index.bundle.js"
                 :provides ["jss"
                            "jss-preset-default"
                            "react"
                            "react-dom"
                            "react-transition-group"]
                 :global-exports {jss jss
                                  jss-preset-default jssPresetDefault
                                  react React
                                  react-dom ReactDOM
                                  react-transition-group ReactTransitionGroup}}]}

webpack.config.js

module.exports = {
  entry: './src/js/index.js',
  output: {
    filename: 'index.bundle.js'
  }
}