Add "sideEffects": false to enable tree-shaking

[arzafran]

Context

I maintain @darkroomengineering/fitbox, a text-fitting library built on pretext. We import only four symbols from the main entry:

import {
  prepareWithSegments,
  measureNaturalWidth,
  measureLineStats,
  layoutWithLines,
} from '@chenglou/pretext';

Observation

package.json doesn't declare "sideEffects": false, so downstream bundlers (Vite/webpack/rollup) conservatively ship the full transitive closure of pretext's internal modules:

File	Size (raw)
analysis.js	37 KB
line-break.js	33 KB
generated/bidi-data.js	23 KB
layout.js	22 KB
measurement.js	8 KB
bidi.js	6 KB
Total	~129 KB raw

Every downstream consumer ships all 129 KB, even when they exercise only a fraction of the exported surface.

Ask

{ "sideEffects": false }

A scan of dist/*.js shows only top-level const/let initialization (regexes, Sets, let sharedWordSegmenter = null). All pure expressions, safe to mark side-effect-free. With the flag, bundlers can drop unused exports based on what consumers actually import (e.g., the seven layout.d.ts exports fitbox doesn't use, plus unused helpers in analysis.js/line-break.js).

Realistic impact: 20–40% bundle reduction for consumers using a subset of the API, which is most of them.

Secondary (lower priority, separate issue if interested)

generated/bidi-data.js is 23 KB of Unicode data needed only for RTL text. If bidi.js could lazy-load it (dynamic import() gated on a quick RTL scan), latin-only sites would drop 23 KB automatically. Not worth tackling until the sideEffects change is measured.

Willing to PR

Happy to open a one-line PR for the sideEffects change, plus a small bundle-size regression test if that's welcome.

[pheobeayo]

Hello, Can I take up this issue?

[mvanhorn]

Submitted in #160 - one-line "sideEffects": false in package.json. Verified all 103 tests pass and no source-code changes.

[chenglou]

Thanks for the clear bundle-size report. Landed this on main in dea8592: the package is now marked side-effect-free for bundlers, and demos/assets still ship in the npm package as reference examples but are no longer package subpath exports.