I like to look at API specs to clear questions like this, e.g.

https://wicg.github.io/shape-detection-api/#barcode-detectio... BarcodeDetector#detect returns a sequence of detected barcodes, so depending on the implementation and input quality it should able to extract multiple barcodes.

https://wicg.github.io/shape-detection-api/#dictdef-detected... each DetectedBarcode has boundingBox/cornerPoints.