what does the “modules:auto” means in @babel/preset-env field?

Question

the babel docs say the modules default option is auto, what does the auto means? does it transform the "import" to "require" or not? what's the difference between "modules: false" and "modules: auto"? it seems they are the same result; I'm learning tree shaking, when I didn't set any options to my @babel/preset-env, tree shaking success, when I set "modules: false", the tree shaking also succeed;

  "presets": [
    [
      "@babel/preset-react"
    ],
    [
      "@babel/preset-env",{"modules": "false"}
    ]
  ],

Answer 1

auto means default value and default value of modules is false. See - https://github.com/babel/babel/pull/8485/files#r236086742.

Answer 2

It seems that the documentation for auto is described in this pull request. According to that PR:

The default auto will automatically select false if ES6 module syntax is already supported by the caller, or "commonjs" otherwise.

So, if ES6 is supported (which seems to be your case) setting modules to auto its the same as setting false.

Answer 3

it enable transformation of ES6 module syntax to another module type.

Reference : https://babeljs.io/docs/en/babel-preset-env#modules