Converting callbacks to async channels

callbacks-to-async-channels.cljs

(ns kanalid.core
  ; (:require-macros [cljs.core.async.macros :refer [go go-loop]])
  (:require [cljs.core.async :refer [go <! put!] :as async]
            ["events" :as EventEmitter]))

(def global-emitter (new EventEmitter))

(defn emit [event data]
  (.emit global-emitter event data))

(defn subscribe
  "Returns JavaScript EventEmitter that emits strings"
  [emitter event-name callback]
  (.addListener emitter event-name callback)
  emitter)

(defn subscribe->channel [emitter event-name]
  (let [channel (async/chan)]
    (subscribe emitter event-name #(put! channel %))
    channel))

(defn example []
  (let [channel (async/chan)
        emitter (new EventEmitter)
        event-name :happening]
    (.addListener emitter event-name #(put! channel %))
    (.emit emitter event-name 42)
    (.emit emitter event-name "Wadiis")
    (async/go-loop []
      (let [val-from-channel (<! channel)]
        (println "Got value from ze channel: " val-from-channel)
        (recur)))
    (println "Done in let"))
  (println "Done in example"))

(defn example-two []
  (let [jobs-channel (subscribe->channel global-emitter :create-job)]
    (go
      (emit :create-job 42)
      (println "Got a new value: " (<! jobs-channel))
      )))

(defn main []
  (println "Hello world!")
  (example)
  (example-two))

shadow-cljs.edn

;; shadow-cljs configuration
{:source-paths
 ["src/dev"
  "src/main"
  "src/test"]

 :dependencies
 []

 :builds
 {:server {:target :node-script
           :main kanalid.core/main
           :output-to "out/kanalid.js"}}}

usage.md

1. Watch the build shadow-cljs watch server
2. Run the code node out/kanalid.js