Shadow CLJS require ES Module in script

01-README.md

This shows how to require ES modules in a node script which is itself compiled as an ES module by shadow. I made this to verify if nbb's way of requiring ES modules aligns with other tools that accomplish the same using the CLJS compiler.

Build with npx shadow-cljs compile script. Run with node out/script.js. It will print something like:

#js {:columns 202, :rows 45}
[Function: Spinner]

package.json

{
  "dependencies": {
    "ink-spinner": "^4.0.2",
    "react": "^16.14.0",
    "shadow-cljs": "^2.15.6",
    "term-size": "^3.0.0",
    "ws": "^8.2.1"
  },
  "type": "module"
}

shadow-cljs.edn

{:source-paths ["src"]
 :builds
 {:script
  {:target :esm
   :output-dir "out"
   :js-options {:keep-as-import #{"term-size" "ink-spinner"}}
   :modules {:script {:init-fn hello.world/main}}}}}

world.cljs

;; place this file in src/hello/world.cljs

(ns hello.world
  (:require ["ink-spinner$default.default" :as is] ;; the double default is weird, but it's the only way that worked for me
            ["term-size$default" :as term-size]))

(defn main []
  (prn (term-size))
  (.log js/console is))

The "ink-spinner$default.default" can be explained by the package being written in typescript but only published as commonjs.

https://unpkg.com/browse/[email protected]/build/index.js

In the early days of commonjs <-> esm interop webpack and others did some "smart" detection as to seemingly make interop easier. See the __esModule marker which was used to make commonjs look like ESM as in it allowed import { thing } from "actually-commonjs". node never did such tricks and only allows import thing from "actually-commonjs". So only one default import which is the object exported by the package, which again only has the default property.

To get this sample working, I ran:
yarn add ink