NativeScript is in beta and currently the NativeScript API exposes the standard platform libraries only, i.e. buttons, widgets and so on. Third-party library support is planned but not implemented yet. So even if you have a third party library for barcode reading, you cannot currently use it through NativeScript.
NativeScript has nothing in with Cordova, so the answer to the second question would be no.
Take a look at this
to learn what NativeScript is.
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