html-crush bug fixed

by — posted on

One line in Babel config, env preset's loose set to true opens in a new tab was causing a spread operator to disappear on only CommonJS builds (not ES Modules or UMD), which led to broken logic (program could not calculate opts.breakToTheLeftOf correctly any more), program inserted extra blank lines. A crazy bug, isn't it?

§ Situation

The html-crush TypeScript source:

if (Array.isArray(opts.breakToTheLeftOf) && opts.breakToTheLeftOf.length) {
breakToTheLeftOfFirstLetters = [ Set( => val[0])),

used to get transpiled into ESM (ES Modules, code with import/export):

if (Array.isArray(opts.breakToTheLeftOf) && opts.breakToTheLeftOf.length) {
breakToTheLeftOfFirstLetters = [ Set( => val[0]))].join("");

but, CJS (CommonJS, code with require) was transpiled into:

if (Array.isArray(opts.breakToTheLeftOf) && opts.breakToTheLeftOf.length) {
breakToTheLeftOfFirstLetters = [].concat(new Set( (val) {
return val[0];

The ..., ES6 spread operator disappears!!!

§ Cause

It was just mis-configured Babel, loose: true, line below:

// babel.config.js
const { NODE_ENV } = process.env;

module.exports = {
presets: [
targets: {
browsers: ["ie >= 11"],
exclude: ["transform-async-to-generator", "transform-regenerator"],
modules: false,
loose: true, // <----------- !!!
plugins: [
NODE_ENV === "test" && "@babel/transform-modules-commonjs",

Once loose is disabled, all works fine again!

By the way, Babel documentation opens in a new tab describes loose very briefly:

Enable "loose" transformations for any plugins in this preset that allow them.

I didn't expect this.

§ Learning

Especially for large, important open source packages, in unit tests, it's wise to test all the builds: ESM, UMD and CJS. "If it quacks like a duck..." — there are no mysteries in programs, either tests pass, or they don't. In theory, unit-testing all builds should safeguard against errors in the build configs. I set up every single unit test in html-crush to check all three builds: UMD, CJS and ESM.

§ Conclusion

Thanks for Romain Vincent opens in a new tab for raising the GitHub issue opens in a new tab. And sorry to everybody who encountered it.

Related packages:

📦 html-crush 4.1.8
Minifies HTML/CSS: valid or broken, pure or mixed with other languages
📦 babel opens in a new tab
Turn ES6 code into readable vanilla ES5 with source maps