Allow using browserlistsrc for targets

[timkelty]

Resolves #1141

Allows users to pass false to options.targets or options.targets.browsers to have babel-env use a .browserlistsrc file.

[eliperelman]

LGTM, @edmorley?

[eliperelman]

Can you revert the change to this line?

[timkelty]

Whups

[timkelty]

Whoopsiedaisy

[edmorley]

Thank you for the PR :-)

[edmorley]

For options.targets.browsers to be false, they would have had to set it themselves as false, since targets defaults to {}. For "I want babel to just use its own logic" I think getting people to always use targets: false might make more sense?

[timkelty]

Yeah - I did it this way because it seemed like options.targets had other props besides browsers that maybe you'd want to set, but still use the browerslistrc. Not totally sure of that's valid though, will have to check when I'm back on a machine: https://babeljs.io/docs/en/babel-preset-env#options

[timkelty]

@edmorley I think you're right – we only need to support options.targets as false, not options.targets.browsers.

Updated PR.

I also moved the defaults for the browsers up to the top with the other defaults.

[timkelty]

Actually, if we set the defaults up-top like this, we don't even need to account for false, and have users just pass {} if they want to overrides defaults.

Just passes things directly to @babel/preset-env with an overridable default.
Seem simpler. Thoughts?

[edmorley]

Seem simpler. Thoughts?

The preset default options are merged with the ones the user passes using deepmerge, so I think the new implementation will prevent people from overriding. Some tests would confirm and likely be useful edither way :-)

[timkelty]

The preset default options are merged with the ones the user passes using deepmerge, so I think the new implementation will prevent people from overriding

@edmorley right you were :) Reverted that and added some tests.

[edmorley]

This looks great - thank you!