devsetup1-6  Exercise 3: An npm Project, npm ci, and Global Tools
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PART 1: A PROJECT WITH A DEPENDENCY
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    mkdir -p ~/projects/npm-demo && cd ~/projects/npm-demo
    npm init -y
    npm install lodash

Create index.js:

    const _ = require('lodash');
    console.log(_.chunk([1, 2, 3, 4, 5], 2));

Run it:

    node index.js
    # [ [ 1, 2 ], [ 3, 4 ], [ 5 ] ]

Look at what npm created:

    ls
    # index.js  node_modules  package-lock.json  package.json
    cat package.json          # lodash listed under "dependencies"

PART 2: DISPOSABLE node_modules
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    rm -rf node_modules
    node index.js             # fails: Cannot find module 'lodash'
    npm ci
    node index.js             # works again

npm ci reads package-lock.json and installs exactly the versions recorded
there, into a fresh node_modules. It is the right command for a clean rebuild
(and for automated builds), because npm install may update versions within the
ranges allowed in package.json. If package.json and the lock file disagree,
npm ci stops with an error instead of quietly changing anything, which is what
you want from a reproducible install.

Add a .gitignore containing:
    node_modules/
so the folder is never committed. Commit package.json and package-lock.json.

PART 3: A GLOBAL TOOL AND A VERSION SWITCH
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    nvm use 24               # or whichever version is your default
    npm install -g cowsay
    npm ls -g --depth=0      # cowsay is listed
    command -v cowsay        # a path under ~/.nvm/versions/node/v24.../bin
    cowsay "hello from devserver"

Now switch:

    nvm use 22
    command -v cowsay        # nothing printed: the tool "vanished"
    npm ls -g --depth=0      # cowsay is not listed under Node 22

EXPLANATION
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nvm keeps a separate set of global packages for each Node version. cowsay was
installed under Node 24's directory, and Node 22 has its own, which does not
contain it. Nothing was lost. Running nvm use 24 brings it back.

TWO WAYS TO FIX IT
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1. Install it again under the other version:  nvm use 22 && npm install -g cowsay
2. Carry your global tools across when adding a version:
       nvm install --reinstall-packages-from=current 22
   (or, between versions already installed, nvm use 22 then
   nvm reinstall-packages 24).

BETTER STILL
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For anything a project needs, put it in that project's package.json (and use
npx for one-off runs), so it does not depend on a global copy or on which Node
version happens to be active.

WHY THIS WORKS AS AN ANSWER
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Part 2 shows the lock file is the record and node_modules is disposable. Part
3 explains a confusing behaviour with a real demonstration, and points to the
practice that avoids the confusion altogether.