My team was trying to get a JS solution working as well, using zxing-js. The barcode basically had to be perfect size, on a flat surface and no glare. we ended up swapping it out for ScandIT's Web SDK and have been very please with performance. As someone else said, it is quite expensive and being a public-facing web application, we had to get a per-scan license vs device license. We're going under contract for 1 year with a "shot in the dark" scan estimate and will renegotiate next year once we have usage statistics.

Would be nice to see if this new spec gets full adoption so we can avoid high licensing fees.