How to use Babel preset with Expo

[songpola]

I want to use @rnx-kit/babel-preset-metro-react-native with Expo.
But Expo already has existing babel-preset-expo.
Both have stated that they're a drop-in replacement for metro-react-native-babel-preset.

So, should I use only one:
{ "presets": ["@rnx-kit/babel-preset-metro-react-native"] },

or should I use both at the same time?
{ "presets": ["babel-preset-expo", "@rnx-kit/babel-preset-metro-react-native"] },

(Also in which order?)
{ "presets": ["@rnx-kit/babel-preset-metro-react-native", "babel-preset-expo"] },

[tido64]

Had a quick look at babel-preset-expo, it looks like it imports metro-react-native-babel-preset and adds more things on top of it. @rnx-kit/babel-preset-metro-react-native does the same thing. If you use both, we cannot guarantee that the same version of metro-react-native-babel-preset is used for both. Since you're using Expo, I would stick to only using babel-preset-expo, and only add what you need from @rnx-kit/babel-preset-metro-react-native. If you know what you need from it, we can at least make it easier for you to import those things.

[songpola]

What @rnx-kit/babel-preset-metro-react-native has and babel-preset-expo does not?
I mean. what would I need from @rnx-kit/babel-preset-metro-react-native if it does the same thing as babel-preset-expo ?

[tido64]

To be honest, I haven't looked very closely so I don't know. I assumed that since you wanted to add @rnx-kit/babel-preset-metro-react-native that you found something useful in there. 😅

[songpola]

Sorry for very late reply. I finally figured out why I need to use @rnx-kit/babel-preset-metro-react-native in the first place.
It because I want to use @rnx-kit/metro-config and it shows that I need that Babel preset. (Docs)
So, I wonder what does the Babel preset really do?
Can I use @rnx-kit/metro-config without it? (Using Expo's instead.)

[tido64]

Right, that looks wrong. You should be able to use @rnx-kit/metro-config without the Babel preset. If it doesn't work, let us know so we can fix it.

Edit: Updated docs: #2770