Challenge 1: Tree Shaking the Five-Function Utils Module — Possible Solution
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WHAT TREE SHAKING DOES HERE
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Per this chapter's own example, utils.js exports five functions
(formatDate, formatPrice, slugify, debounce, throttle), but app.js
only imports two of them: formatPrice and slugify. Tree shaking
analyzes the whole reachable dependency graph (build-tooling1-2) and
determines that formatDate, debounce, and throttle are never actually
imported by anything reachable from the entry point. Since nothing
uses them, the bundler safely removes them (and any dependencies THEY
alone would have needed) from the final output entirely — only
formatPrice, slugify, and whatever those two specifically depend on
end up in the shipped bundle.

WHY THIS ONLY WORKS RELIABLY BECAUSE THE IMPORT IS ESM
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Per build-tooling1-2's own explanation, ES Modules' import statements
are static — required to sit at the top level of a file, with a
fixed, literal specifier, never conditional or computed. This means
the bundler can determine, with total certainty, by parsing app.js's
text alone, that exactly formatPrice and slugify are imported and
nothing else — there's no way a hidden runtime condition could later
reveal that formatDate is secretly needed after all.

If app.js had instead used CommonJS's require() to pull in utils.js,
that certainty would disappear: require() calls can be dynamic or
conditional (per build-tooling1-2's own dynamic-require example), so
a bundler could never be fully sure whether some other, less obvious
code path might actually need formatDate, debounce, or throttle at
runtime. Removing them in that case would be a genuine risk, not a
safe, certain optimization — which is exactly why CommonJS code can't
be tree-shaken with the same confidence ESM code can.

WHY THIS WORKS AS AN ANSWER
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It applies tree shaking to the specific example given (correctly
identifying which three functions get removed), and explains the ESM-
specific certainty (static, non-conditional imports) that makes the
removal provably safe, contrasted against what would go wrong if the
same code used CommonJS instead.