Providing function() from application to library

I have a class AppComponent in my application that has these functions:

scan(){
var success = function(result) {
alert(JSON.stringify(result.text, undefined, 2));
}
var failure = function(result) {
alert(JSON.stringify(result.text, undefined, 2));
}
cordova.plugins.BarcodeScanner.scan(success, failure, [])
}


My library provides the pages for my application, but I cannot add this function inside the library, because not every user of it needs the barcode scanner.

My question: how can I dependency inject this function on a non-essential basis?

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