Exercise 1: Why the Component Reappears Unchanged — Possible Solution
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WHY IT REAPPEARS UNCHANGED
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The useBarcodeScanner hook built in this chapter has no knowledge of Firebase, Firestore, or Cloud Functions at all - it only requests camera access, decodes barcodes from the video feed, and calls one callback, onDetected(barcode), with the result. Since it never references anything specific to this course's own backend, the exact same hook and video-rendering component can be dropped into Food Tracker (React + Express) with no modification needed.

THE ONE THING THAT ACTUALLY DIFFERS
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The parent component's own handleDetected callback - specifically, what it does with the barcode once it has one. In this course, handleDetected calls Chapter 3's lookupBarcode Cloud Function. In Food Tracker (React + Express), the equivalent handleDetected would instead call that course's own Express server's POST endpoint. Everything else - the camera access, the detection loop, the cleanup logic - stays identical.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies that the scanning component is backend-agnostic because it only exposes a single callback with no awareness of what's on the other end, and correctly names the parent component's callback implementation as the one and only thing that differs between the two sibling courses' usage of it.