creating shell scripts with node/esm

intro

Learn how to create an executable standalone script two different ways:

• node/esm
• npm package + node/esm

The finished package is available here:

• On GitHub as @frankg/demo
• On npm as @frankg/demo

node/esm as a standalone shell script

FILE EXTENSIONS

• .mjs interpreted as esm
• .js interpreted as esm when you include "type": "module" in package.json

Since we're creating a standalone script we don't have package.json we use .mjs

import * as os from "node:os";

const { username } = os.userInfo();
console.log(`Hello ${username}!`);

RUNNING WITH NODE

• node hello.mjs

RUNNING STANDALONE

• edit script

#!/usr/bin/env node
import * as os from "node:os";

const { username } = os.userInfo();
console.log(`Hello ${username}!`);

• make it executable -- chmod u+x hello.mjs
• run it ./hello.mjs

node/esm as an npm package

creating the files

• create directory mkdir demo; cd demo
• create package.json file npm init -y
• add dependencies pn add lodash-es -- creates node_modules folder and package-lock.json file
• add readme.md file
• add add two shell scripts

    demo/
        package.json
        package-lock.json
        readme.md
        src/
            homedir.mjs
            versions.mjs

• add content to package.json

  ...
  "type": "module",
  "bin": {
    "homedir": "./src/homedir.mjs",
    "versions": "./src/versions.mjs"
  },
  ...

• package.json contents -- confirm required publishing fields: name, version, license

{
  "name": "esm-executable",
  "version": "1.0.0",
  "description": "## intro",
  "main": "index.js",
  "type": "module",
  "bin": {
    "homedir": "./src/homedir.mjs",
    "versions": "./src/versions.mjs"
  },
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "MIT",
  "dependencies": {
    "lodash-es": "^4.17.21"
  }
}

• populate homedir.mjs -- you can run with node ./src/homedir.mjs

#!/usr/bin/env node
import { homedir } from "node:os";

console.log("Homedir: " + homedir());

• populate versions.mjs -- you can run with node ./src/versions.mjs

#!/usr/bin/env node

import { pick } from "lodash-es";

console.log(pick(process.versions, ["node", "v8", "unicode"]));

how npm runs shell scripts

INSTALLING ON UNIX

A script such as homedir.mjs does not need to be executable on Unix because npm installs it via an executable symbolic link:

• when installing the package globally, the link is added to a directory that’s listed in $PATH.
• when installing the package locally (as a dependency), the link is added to node_modules/.bin/

publishing the package

Before we publish lets check the configuration

• .gitignore is honored
• .npmignore overides .gitignore
• see files excluded by default:

exclude by default

node_modules
.*.swp
._*
.DS_Store
.git
.gitignore
.npmignore
.npmrc
npm-debug.log

never exclude

package.json
README.md and its variants
CHANGELOG and its variants
LICENSE, LICENCE

Here are some things we can check

• check which files will be uploaded npm publish --dry-run
• create an archive package as it's store on the registry npm pack
• install globally with either of these two: npm link or npm install . -g
• list globally installed packages npm ls -g -- see the package-name
• create an npm account if needed
• upload to the registry npm publish --access public - access only needed first time
• change access level if needed
• a new version is required for every upload -- use semver - major.minor.patch

avoiding the .mjs extension

Here's a magic trick to avoid having to use the .mjs extension throught your code.

• prepend your shell script files with the following snippet:

#!/bin/sh
":"; // ; cat "$0" | node --input-type=module - $@ ; exit $?

UPDATE: I took out the snippet and it still works with this

#!/usr/bin/env node

# see the package installed
npm ls -g

...
├── [email protected] -> ./../../../../../dev/code/scratch/typescript/esm-executable
...

# find the node path
which node

/Users/frankg/.nvm/versions/node/v18.15.0/bin/node


# show the executable shell scripts
ls /Users/frankg/.nvm/versions/node/v18.15.0/bin

lrwxr-xr-x  1 frankg  staff    49B Sep 11 03:53 homedir -> ../lib/node_modules/esm-executable/src/homedir.js
lrwxr-xr-x  1 frankg  staff    50B Sep 11 03:53 versions -> ../lib/node_modules/esm-executable/src/versions.js