Clojure Scripting on Node.js

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Try it out

Run npx nbb to run nbb on your own machine, or try it in a browser on Replit!

Goals and features

Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.

Additional goals and features are:

• Fast startup without relying on a custom version of Node.js.
• Small artifact (current size is around 1.2MB).
• First class macros.
• Support building small TUI apps using Reagent.
• Complement babashka with libraries from the Node.js ecosystem.

Community

Requirements

Nbb requires Node.js v14 or newer.

How does this tool work?

CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).

Usage

Install nbb from NPM:

Omit -g for a local install.

Try out an expression:

And then install some other NPM libraries to use in the script. E.g. with the following package.json:

{
  "dependencies": {
    "csv-parse": "^5.0.4",
    "shelljs": "^0.8.5",
    "term-size": "^3.0.1",
    "zx": "^5.3.0"
  }
}

Create a script which uses the NPM libraries:

(ns example
  (:require ["csv-parse/sync$default" :as csv]
            ["fs" :as fs]
            ["path" :as path]
            ["shelljs$default" :as sh]
            ["term-size$default" :as term-size]
            ["zx" :refer [$]]
            ["zx$fs" :as zxfs]
            [nbb.core :refer [*file*]]))

(prn (path/resolve "."))

(prn (term-size))

(println (count (str (fs/readFileSync *file*))))

(prn (sh/ls "."))

(prn (csv/parse "foo,bar"))

(prn (zxfs/existsSync *file*))

($ #js ["ls"])

Call the script:

$ nbb script.cljs
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs

What does $default mean?

The :default foo syntax is shadow-cljs only and not supported by vanilla CLJS (and nbb doesn't support it either). The $default syntax is a recent addition to CLJS and should work in shadow-cljs too: this is why nbb supports it too.

See here for more info on that syntax.

Nbb implements :require via dynamic import (import() in JS). This is why you need to add $default to imports when you want to import the default object from a module.

Macros

Nbb has first class support for macros: you can define them right inside your .cljs file, like you are used to from JVM Clojure. Consider the plet macro to make working with promises more palatable:

(defmacro plet
  [bindings & body]
  (let [binding-pairs (reverse (partition 2 bindings))
        body (cons 'do body)]
    (reduce (fn [body [sym expr]]
              (let [expr (list '.resolve 'js/Promise expr)]
                (list '.then expr (list 'clojure.core/fn (vector sym)
                                        body))))
            body
            binding-pairs)))

Using this macro we can make async code look more like sync code. Consider this puppeteer example:

(-> (.launch puppeteer)
      (.then (fn [browser]
               (-> (.newPage browser)
                   (.then (fn [page]
                            (-> (.goto page "https://clojure.org")
                                (.then #(.screenshot page #js{:path "screenshot.png"}))
                                (.catch #(js/console.log %))
                                (.then #(.close browser)))))))))

Using plet this becomes:

(plet [browser (.launch puppeteer)
       page (.newPage browser)
       _ (.goto page "https://clojure.org")
       _ (-> (.screenshot page #js{:path "screenshot.png"})
             (.catch #(js/console.log %)))]
      (.close browser))

See the puppeteer example for the full code.

Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet macro is similar to promesa.core/let.

Startup time

$ time nbb -e '(+ 1 2 3)'
6
nbb -e '(+ 1 2 3)'   0.17s  user 0.02s system 109% cpu 0.168 total

The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx this adds another 300ms or so, so for faster startup, either use a globally installed nbb or use $(npm bin)/nbb script.cljs to bypass npx.

Dependencies

NPM dependencies

Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.

Classpath

To load .cljs files from local paths or dependencies, you can use the --classpath argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs relative to your current dir, then you can load it via (:require [foo.bar :as fb]). Note that nbb uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar in the namespace name becomes foo_bar in the directory name.

To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:

$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"

and then feed it to the --classpath argument:

$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]

Currently nbb only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar files will be added later. You can find a workaround for that here.

Current file

The name of the file that is currently being executed is available via nbb.core/*file* or on the metadata of vars:

(ns foo
  (:require [nbb.core :refer [*file*]]))

(prn *file*) ;; "/private/tmp/foo.cljs"

(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"

Reagent

Nbb includes reagent.core which will be lazily loaded when required. You can use this together with ink to create a TUI application:

ink-demo.cljs:

(ns ink-demo
  (:require ["ink" :refer [render Text]]
            [reagent.core :as r]))

(defonce state (r/atom 0))

(doseq [n (range 1 11)]
  (js/setTimeout #(swap! state inc) (* n 500)))

(defn hello []
  [:> Text {:color "green"} "Hello, world! " @state])

(render (r/as-element [hello]))

Working with promises

Promesa

Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core namespace is included with the let and do! macros. An example:

(ns prom
  (:require [promesa.core :as p]))

(defn sleep [ms]
  (js/Promise.
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
  []
  (p/do!
   (println "Doing stuff which takes a while")
   (sleep 1000)
   1))

(p/let [a (do-stuff)
        b (inc a)
        c (do-stuff)
        d (+ b c)]
  (prn d))

$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while
3

Also see API docs.

REPL

In the REPL it can be convenient to bind the resolved value of promises to a var. You can do that like this:

(defmacro defp [binding expr]
  `(-> ~expr (.then (fn [val]
                     (def ~binding val)))))

(defp browser (.launch puppeteer #js {:headless false}))
(defp page (.newPage browser))
(.goto page "https://clojure.org")

Cljs-bean

Since nbb v0.1.0 cljs-bean is available.

See the example for an example.

Js-interop

Since nbb v0.0.75 applied-science/js-interop is available:

(ns example
  (:require [applied-science.js-interop :as j]))

(def o (j/lit {:a 1 :b 2 :c {:d 1}}))

(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1

Most of this library is supported in nbb, except the following:

• destructuring using :syms
• property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.

Reader conditionals

Nbb supports the following reader conditional features: :org.babashka/nbb and :cljs in that order of priority:

#?(:org.babashka/nbb 1 :cljs 2) ;;=> 1
#?(:cljs 2 :org.babashka/nbb 1) ;;=> 2

Main function

It is possible to use the -main function as the software (script) start point when using the m parameter of nbb passing your software namespace.

(ns example)

(defn -main
  [& args]
  (prn "print in -main"))

Execute:

Testing

See doc/testing.

REPL

Console REPL

To start a console REPL, simply run nbb.

Socket REPL

To start a socket server REPL, run:

$ nbb socket-repl :port 1337

REPL API

Nbb exposes the nbb.repl namespace to programmatically start a REPL. See API for more info. An example:

(ns example
  (:require [nbb.repl :as repl]
            [promesa.core :as p]))

(defn available-in-repl [] :yolo)

(p/do!
 (repl/repl)
 ;; type (available-in-repl) in the REPL and it will return :yolo
 (println "The end"))

The repl function returns a promise. The promesa.core/do! macro waits for the REPL to finish and after that "The end" is printed:

$ nbb example.cljs
example=> (available-in-repl)
:yolo
example=> The end

To launch a REPL from a Node.js script, you can use loadString or loadFile:

import { loadString } from 'nbb'
await loadString(`
(require '[nbb.repl :refer [repl]])
(repl)
`)
console.log('The end!')

$ node repl.mjs
user=> (+ 1 2 3)
6
user=> The end!

nREPL

The nREPL server probably still has rough edges. Please report issues here.

An nREPL server can be started with:

$ nbb nrepl-server :port 1337

After that you can connect using an nREPL client:

$ lein repl :connect 1337

and evaluate expressions.

Running nREPL in Docker container is supported with the optional :host argument.

$ nbb nrepl-server :port 1337 :host 0.0.0.0

Calva

In Calva connect to the REPL with:

• Connect to a Running REPL Server not in Project > ClojureScript nREPL server

CIDER

Currently CIDER needs the following workaround.

Vim Iced

See this tweet.

Projects using nbb

The following projects are using nbb or are supporting it as a development platform:

Examples

API

See API documentation with a list of built-in libraries.

Videos

Articles

Podcasts

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.

Publishing an nbb project to npm

See Publishing an nbb project to npm.

Creating a standalone executable with caxa

See Creating a standalone executable with caxa.

Nbb on AWS Lambda

See Nbb on AWS Lambda.

Nbb on Google Cloud Functions

See Nbb on Google Cloud Functions.

Nbb on fly.io

See Deploying an nbb app to fly.io.

Build

Prequisites:

• babashka >= 0.4.0
• Clojure CLI >= 1.10.3.933
• Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

• Clone and cd into this repo
• bb release

Run bb tasks for more project-related tasks.

Credits

• Original babashka logo by Nikita Prokopov. Node.js modifications by MnRa.

License

Copyright © 2021-2022 Michiel Borkent

Distributed under the EPL License. See LICENSE.

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