fix: search for browserslist if esmodules is falsy

[fengzilong]

Q	A
Fixed Issues?	Fixes #11123
Patch: Bug Fix?	Yes
Major: Breaking Change?	Maybe for some user
Minor: New Feature?	No
Tests Added + Pass?	No
Documentation PR Link	No
Any Dependency Changes?	No
License	MIT

As stated in issue #11123, with targets

{
  presets: [
    [
      '@babel/preset-env',
      {
        targets: {
          esmodules: false
        }
      }
    ]
  ]
}

babel won't search for browserslist config

[JLHwung]

I think we should normalize target { esmodules: false } to {} in

babel/packages/babel-preset-env/src/normalize-options.js

Line 121 in 157bb6e

const normalizeTargets = targets => {

so if target.esmodules is accessed later, if must be true and we don't have to worry that it can be false or any other fancy falsy values.

[fengzilong]

Hmmm...what I worry about is that some package use babel-helper-compilation-targets directly, e.g. @vue/babel-preset-app. should we fix the bug for those packages

https://github.com/vuejs/vue-cli/blob/c8cecffedbf7b19cf930bb2821b5c352bc716a67/packages/%40vue/babel-preset-app/index.js#L17

[JLHwung]

I see. Since target.esmodules is used as a shortcut to set target.browsers to be those with esmoduels support. We can delete it after it is consumed.

[fengzilong]

Seems reasonable ❤️. Updated

[JLHwung]

Thanks!

[nicolo-ribaudo]

Should we also delete it if it is truthy, since at this point we have already handled it?

[fengzilong]

User may invoke this method twice or more, keep the truthy value is safer for this case

const getTargets = require( '@babel/helper-compilation-targets' ).default
const targets = { esmodules: true }
const result1 = getTargets( targets )
const result2 = getTargets( targets )
// result1 should be equal to result2 here

[nicolo-ribaudo]

Wouldn't they still be the same?

After the first call, targets has a browsers property which makes its behaviour identical to esmodules: true.

[fengzilong]

Oops, sorry I didn't realize targets.browsers have already been assigned to targets. Updated

[nicolo-ribaudo]

Thanks!