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

Submit bugs at Github Issues.
Join Github Discussions for proposing ideas, show and tell and Q&A.
Join the channel on Clojurians Slack.
Follow news or tweet using the Twitter hashtag #nbbjs.

Requirements

Nbb requires Node.js v14 or newer.

Additionally, in the case of downloading Clojure dependencies, it requires the installation of babashka.

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:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'
6

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

{
  "dependencies": {
    "csv-parse": "^5.3.0",
    "shelljs": "^0.8.5",
    "term-size": "^3.0.2",
    "zx": "^7.1.1"
  }
}

Create a script which uses the NPM libraries:

(ns example
  (:require ["csv-parse/sync" :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.

Libraries

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

Dependencies

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.

Clojure dependencies

Note: this feature relies on the presence of the babashka bb executable in the system's PATH.

To load dependencies from the Clojure ecosystem, you can create an nbb.edn:

{:deps {com.github.seancorfield/honeysql {:mvn/version "2.2.868"}}}

Similar to node_modules, nbb will unpack these dependencies in an .nbb directory and will load them from there.

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.

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"

In Python scripts there is a well-known pattern to check if the current file was the file invoked from the command line, or loaded from another file: the name == "main" pattern. In nbb this pattern can be implemented with:

(= nbb.core/*file* (nbb.core/invoked-file))

Reagent

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

$ npm install ink

ink-demo.cljs:

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

(defonce state (r/atom 0))

(def count
  (js/setInterval
   #(if (< @state 10)
      (swap! state inc)
      (js/clearInterval count))
   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.

<!-- Since nbb v0.5.110 [

Nbb

Install / Use

README