Challenge 2: Why CommonJS Packages Can't Load via <script src> — Possible Solution
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WHAT COMMONJS ACTUALLY REQUIRES
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Per node1-2, CommonJS's require() function works by resolving a
module specifier (like 'lodash' or './utils') into an actual file on
disk, using Node's own file-system-based module resolution algorithm
— searching node_modules directories, resolving relative paths,
reading package.json's own "main" field, and so on. module.exports
then makes that file's own exported values available to whatever
called require() on it.

WHY A BROWSER CAN'T DO THIS
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Per this chapter's own explanation, a browser tab has no access to a
local file system to search through in the way Node's own require()
resolution depends on — there is no node_modules folder sitting
"nearby" for the browser to look through, and no built-in browser
API that implements Node's own file-resolution algorithm. require()
and module.exports are Node-specific globals; they simply don't exist
inside a browser's own JavaScript environment at all. A script
containing require('some-package') that's loaded directly via
<script src> in a browser will fail immediately, because require
itself is undefined there.

WHY THIS MAKES A BUILD STEP NECESSARY, NOT OPTIONAL
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Since the browser has no way to execute CommonJS's own module system
natively, something has to happen BEFORE the code ever reaches the
browser: a bundler has to read each require() call, actually resolve
and locate the corresponding file (doing, at build time, exactly the
resolution work Node would normally do at run time), and merge the
result into a single bundle (or a set of ES-module-compatible
outputs) that no longer contains any require() calls the browser
would fail on. This is exactly why this chapter states plainly that a
build step "isn't optional... once npm packages are involved" — the
translation from CommonJS to browser-runnable code has to happen
somewhere, and the browser itself cannot do it.

WHY THIS WORKS AS AN ANSWER
------------------------------
It explains specifically what require() depends on (Node's own file-
system module resolution) using node1-2's own material, explains
precisely why that dependency doesn't exist in a browser environment,
and connects the gap directly to why a build step is genuinely
required rather than merely convenient.