feat: migrate to native ESM with no build step by matthew-dean · Pull Request #4411 · less/less.js

matthew-dean · 2026-03-09T23:10:48Z

Summary

Rename src/ to lib/ — source files are shipped directly with no compilation step
Native ESM: Added "type": "module" to package.json, targeting Node 18+
No build for Node: The src/ → lib/ transpilation step is removed entirely
Browser build still works: Rollup UMD bundle reads from lib/ directly. Bundle size actually decreased (509KB → 500KB unminified, 158KB → 153KB minified)
CJS files renamed to .cjs: Gruntfile.cjs, .eslintrc.cjs, @plugin test fixtures, and browser generator configs
Stop tracking dist/: Generated browser bundles removed from source control (served via npm/CDN)
CI fixes: fail-fast: false, playwright moved to root devDependencies, pnpm exec for playwright install
All 139 tests pass with no regressions

Key changes

.js extensions added to all relative imports for ESM resolution
createRequire() used for npm package resolution and JSON imports (optional deps like clean-css, source-map)
bin/lessc, test files, and build scripts converted from CJS to ESM
CI matrix updated with fail-fast: false so all jobs run independently

Test plan

All 139 Node.js tests pass (npm test)
Browser build generates successfully (node build/rollup.js --dist)
CLI works (bin/lessc compiles .less files)
Browser test generator works (ESM conversion)
CI passes on ubuntu/macos/windows with Node current, lts/*, lts/-1, lts/-2, lts/-3

- Rename src/ to lib/ — source files are shipped directly, no compilation - Add "type": "module" to package.json for native ESM support (Node 18+) - Convert bin/lessc, test files, and build scripts from CJS to ESM - Rename Gruntfile.js and .eslintrc.js to .cjs (must remain CommonJS) - Add .js extensions to all relative import paths for ESM resolution - Use createRequire() for optional dependency resolution (npm packages, JSON) - Configure TypeScript for check-only mode (noEmit: true, allowJs: true) - Update Rollup config to read from lib/ directly - Update CI matrix to drop Node 16 (minimum Node 18+) - Browser build is smaller: 500KB (was 509KB), minified 153KB (was 158KB) - All 139 tests pass

coderabbitai · 2026-03-09T23:11:11Z

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Generated browser bundles don't need to be in source control — they're built during publish and included in the npm package via the files field. Removes duplicate copies from both root dist/ and packages/less/dist/.

npx doesn't reliably find binaries with pnpm. Since playwright is already a devDependency, use pnpm exec to run the installed version.

pnpm exec at workspace root can't find playwright binary since it's a devDependency of the less package. Use --filter to run in that context. Also disable fail-fast so all matrix jobs complete independently.

Makes pnpm exec playwright work from workspace root in CI.

copy-anything v2 lacks "type": "module", causing named import failures on Node 18. v3 has proper ESM exports. Revert testFolder to absolute path (matching original behavior) so debug test path replacements match Less compiler output on Windows.

…ed package Restricts npm package to only bin/, lib/, dist/, index.js, and README.md. Previously shipped test files, Gruntfile, eslint config, etc. Removes postinstall script (Playwright browser install) which only applies in the monorepo dev environment and fails when installed from npm. Verified: npm pack --dry-run shows 120 files (was 229), lessc CLI and API both work from a clean tarball install.

dosubot Bot added the size:L This PR changes 100-499 lines, ignoring generated files. label Mar 9, 2026

matthew-dean added 10 commits March 9, 2026 16:11

chore: fix trailing semicolons from linter

a451482

chore: gitignore generated .css.map files in lib/

4e1a0ae

fix(ci): restore lts/-3 to test matrix

954c25a

chore: stop tracking dist/ build artifacts

64f4cbf

Generated browser bundles don't need to be in source control — they're built during publish and included in the npm package via the files field. Removes duplicate copies from both root dist/ and packages/less/dist/.

fix(ci): use pnpm exec for playwright install

c294a2b

npx doesn't reliably find binaries with pnpm. Since playwright is already a devDependency, use pnpm exec to run the installed version.

fix(ci): use pnpm --filter for playwright, disable fail-fast

8d900a7

pnpm exec at workspace root can't find playwright binary since it's a devDependency of the less package. Use --filter to run in that context. Also disable fail-fast so all matrix jobs complete independently.

fix(ci): move playwright to root devDependencies

d2d7447

Makes pnpm exec playwright work from workspace root in CI.

chore: add CodeRabbit config to raise file review limit

6696ec5

matthew-dean merged commit c21e465 into less:master Mar 9, 2026
8 checks passed

Cygra mentioned this pull request Mar 11, 2026

LESS 4.6.2 causing build error #4423

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feat: migrate to native ESM with no build step#4411

feat: migrate to native ESM with no build step#4411
matthew-dean merged 11 commits intoless:masterfrom
matthew-dean:esm-migration

matthew-dean commented Mar 9, 2026 •

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matthew-dean commented Mar 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Key changes

Test plan

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matthew-dean commented Mar 9, 2026 •

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