fix: bundle ESM-only deps into CJS output with Rollup

[athenabriana]

What is the motivation for this pull request?

The CJS build (lib/) shipped in v7.0.0 is broken — it require()s dependencies that are now ESM-only.

The problem

In v7.0.0, both direct dependencies were upgraded:

• domhandler v5 → v6 (now ESM-only, "type": "module")
• htmlparser2 v10 → v12 (now ESM-only, also pulls ESM-only domutils@4, domelementtype@3, entities@8)

The CJS build is still compiled with plain tsc --module commonjs, which converts import to require(). Since these dependencies no longer have CJS entry points, this fails:

Error: require() of ES Module .../domhandler/dist/index.js not supported.
ERR_REQUIRE_ESM

Prior to v7, this worked because domhandler@5 and htmlparser2@10 shipped CJS. The package still advertises CJS support via "require": "./lib/index.js" in its exports map.

Affected

• Node.js < 22.12 (includes Node.js 20 LTS, EOL April 2026)
• Vitest (jsdom/happy-dom environments resolve CJS)
• Jest (resolves CJS by default)
• SSR environments using CJS module resolution

Not affected

• Node.js >= 22.12 (require(esm) enabled by default)
• Node.js >= 24
• Bundlers (Webpack, Vite, esbuild — they resolve ESM natively)

The fix

Switch the CJS build from plain tsc to Rollup (which already handles the ESM and UMD builds). Rollup's @rollup/plugin-node-resolve and @rollup/plugin-commonjs plugins bundle the ESM-only dependencies into the CJS output, eliminating the bare require() calls.

Changes:

• scripts/build.sh --cjs: generates declaration files with tsc --emitDeclarationOnly, then bundles CJS with Rollup
• rollup.config.mjs: adds CJS server and client configs (same pattern as the existing ESM configs)

All existing tests pass. No API changes.

Alternative: drop CJS support

If the upgrade to ESM-only dependencies was intentional and CJS support is no longer a goal, this PR can be closed in favor of removing CJS entirely:

• Remove "require" conditions from the "exports" map in package.json
• Remove "main": "./lib/index.js"
• Remove the CJS build step (build:cjs)
• Add "type": "module" to package.json

The current state — advertising CJS via the exports map but shipping a broken CJS build — should be resolved either way.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (fda4c22) to head (901f1b4).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1409   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          120       120           
  Branches        30        30           
=========================================
  Hits           120       120           

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[remarkablemark]

Thanks so much for the fix @athenacfr!

[remarkablemark]

Released:

• chore(master): release 7.0.1 #1410 (comment)