Add ClojureScript hello-world which compiles to Node.js

Author: lambrospetrou

cljs-hello-world/.gitignore

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+build/
+out/
+.cpcache/

cljs-hello-world/README.md

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+# Sample app to generate compile ClojureScript to NodeJS module
+
+The output can be used in AWS Lambda, and in general as a Node.js module.
+
+## Compile with Clojure
+
+```bash
+clj -m cljs.main --target node --optimizations advanced -c hello-world.core
+```
+
+The above generates the `out/` directory which will contain the `main.js` file.
+
+### Compile with Lumo
+
+An alternative way to compiling ClojureScript is using [Lumo](https://github.com/anmonteiro/lumo).
+
+```
+# Download Lumo Docker image or install it on your system
+docker pull anmonteiro/lumo:latest
+
+# Compile command
+docker run -v `pwd`:`pwd` -w `pwd` --rm -it anmonteiro/lumo --classpath src ./build.cljs
+
+# The Docker user by default is root so fix the ownership
+sudo chown -R `id -u`:`id -u` main.js
+```
+
+This will compile the CLJS code and generate the `out/main.js`, as defined in `build.cljs`, which is the same as the one compiled by Clojure.
+
+## Create the AWS Lambda bundle
+
+```
+./build-tools/lambda_bundle.sh
+```
+
+Creates the `build/` directory which will contain the lambda bundle zip.

cljs-hello-world/build-tools/index.js

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+module.exports.handler = require('./main').hello_world.core.handler;

cljs-hello-world/build-tools/lambda_bundle.sh

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+#!/usr/bin/env bash
+
+# Use Clojure to build the ClojureScript function
+clj -m cljs.main --target node --optimizations advanced -c hello-world.core
+# Or use Lumo which is ontop of NodeJS so no need for Java/Clojure.
+# Assumes `docker pull anmonteiro/lumo:latest`
+#docker run -v `pwd`:`pwd` -w `pwd` --rm -it anmonteiro/lumo --classpath src ./build.cljs && chown -R `id -u`:`id -u` main.js
+
+rm -rf build/ && mkdir -p build/
+zip -j build/awslambda.zip build-tools/index.js out/main.js

cljs-hello-world/build.cljs

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+(require '[lumo.build.api :as b])
+
+(b/build "src"
+         {:main 'hello-world.core
+          :output-to "out/main.js"
+          :optimizations :advanced
+          :target :nodejs})

cljs-hello-world/deps.edn

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+{:deps {org.clojure/clojurescript {:mvn/version "1.10.339"}}}

cljs-hello-world/src/hello_world/core.cljs

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+(ns hello-world.core
+  (:require [cljs.nodejs :as nodejs]
+            [clojure.string :as str]))
+
+(nodejs/enable-util-print!)
+(enable-console-print!)
+
+(println "Hello world!")
+
+(defn average [& a]
+  (do
+    (println (str "Calculating average for: " a))
+    (/ (reduce + a) (count a))))
+
+(defn extract-nums [event]
+  (into
+   []
+   (map
+    #(js/parseInt %)
+    (filter #((comp not str/blank?) %) (str/split (get (get event "queryStringParameters") "n" "") #",")))))
+
+(defn ^:export handler [event context callback]
+  (do
+    (println event)
+    (callback
+     nil
+     (clj->js {:statusCode 200
+               :body (.stringify js/JSON (apply average (extract-nums (js->clj event))))
+               :headers {}}))))
+
+; The following only works with `simple` optimizations
+; (set! (.-exports js/module) #js
+      ; {:handler handler})