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This may affect some very corner cases (allowCommonJSExports=false, using e.g. export??=1 and the node version does not support ??= and is not executed), But I don't think anyone does.

I'm not sure I understand, could you give an example? If ?? is not supported, then users would have a plugin to transform it right?

I'm not sure I understand, could you give an example? If ?? is not supported, then users would have a plugin to transform it right?

Yes, users should enable the corresponding plugin.

Technically, in node without ??= support, this will be turned from a hidden error into a thrown error, but I don't think anyone will do that.

if(false) {
  exports ??= {};
}

To be honest, I don't know why we should handle them in module transformation.
Perhaps we can try to change this in Babel 8.
https://github.com/babel/babel/pull/16882/files#diff-5b230a5938b6f7647f17c178c6de6138ba14109652ff7e95a6708d2e6d71a6c6R8-R22