Add sideEffects directive to all package.json

[aduth]

🛠 Summary of changes

Adds (and enforces) the presence of a sideEffects directive within each package's package.json.

Why?

By default, Webpack and other common bundlers assume that any imported code may include side effects, and as such will not aggressively try to perform dead code elimination. Explicitly defining side effects (or the absence of them) allows Webpack to perform this optimization.

See also:

• https://webpack.js.org/guides/tree-shaking/
• https://esbuild.github.io/api/#ignore-annotations

In practice, I noticed this by looking at the platform-authenticator-avaiable-*.js file loaded on https://secure.login.gov/ , which includes the snippet of code new Set(["NotAllowedError", "TimeoutError", "InvalidStateError"]); irrelevant for that bundle.

Performance Impact

yarn build:js

Total JavaScript size:

du -s public/packs/js

Before: 12240kb
After: 12176kb
Diff: -64kb (-0.5%)

Critical path (http://localhost:3000), with gzip enabled:

Before: 6.4kb
After: 6.3kb
Diff: -0.1kb (-1.6%)

Observation: The benefit here isn't as substantial as I might have hoped, and may not warrant the effort involved in maintaining an accurate configuration for every package. I could be open to pushback here. I still think targeting a lack of side effects is ideal, with custom elements being the main point of complication. The savings here could be more substantial in the future depending on future package code revisions.

📜 Testing Plan

1. rm -rf public/packs/js
2. NODE_ENV=production yarn build:js
3. cat public/packs/js/platform-authenticator-available-*.digested.js | grep NotAllowedError
4. echo $?
5. Observe: "1"