tree-shaking: is it still the default behavior of @babel/preset-env to transform es6 to cjs?

[berkant]

Hi.

Quoting from the https://webpack.js.org/guides/tree-shaking/#conclusion,

Ensure no compilers transform your ES2015 module syntax into CommonJS modules (this is the default behavior of the popular Babel preset @babel/preset-env - see the documentation for more details).

However https://babeljs.io/docs/en/babel-preset-env#modules says the default mod is "auto", where the actual value is determined from the caller.

Just wanting to confirm, does docs need a change regarding this?

[alexander-akait]

Yep, feel free to update docs

[nyngwang]

@berkant:
Quoting from the https://webpack.js.org/guides/tree-shaking/#conclusion,

[...]

[...]
Just wanting to confirm, does docs need a change regarding this?

The documentation is no wrong. This is my test for you:

babel.config.js:

presets: [
  [
    '@babel/preset-env', {
      debug: true,
      useBuiltIns: 'usage',
      corejs: 3.21,
      // no `modules: false` here
    },
  ],
// ...

package.json: (I tried to make the target browser as old as possible so that (I think, you can ask @alexander-akait for checking) it should try to transpile to es5 instead of es6.)

"sideEffects": [
  "*.css"
],
"browserslist": [
  "Edge 12"
],

Finally, webpack.config.js.optimization: (I commented out all tree-shaking related hint, but I did add --mode production to webpack CLI-command script)

// usedExports: true,
// sideEffects: true,
// providedExports: true,
minimize: true,

In the result bundle the unused export function square(x) { ... }(I used the example from the webpack's docs.) did get removed.

[JiangWeixian]

thx, project package.json sideEffects field works for me.