The benefit of WASM in this case is that you can wrap a mature library written in C/C++ (in this case, Zint), and run it in a runtime that supports WASM, e.g. the browser. There's plenty of people who occasionally need to create barcodes, and not in some industrial, automated way, and a browser is just an easy way to accomplish that. Yes, you have 1MB loaded when you load the page, but hopefully that will be served from a cache.
As a connoisseur of SVG, I like the approach, the results, the use of Zint and WASM. That said, there are a few opportunities.
The version string isn't needed these days, nor the XML header or the doctype.
The code/url/page title can go in the SVG title, to make it show on mouseover.
The id=barcode is also superfluous. Since id codes should be unique, this could be a problem when many QR codes exist on a page.
The background rectangle does not need x=0, y=0 since that is implied.
The 'hard coding' of the black and white is what you want to avoid any dark mode issues, however, I would still use currentColor and transparent rather than black, just to put myself in a world of dark/light mode pain, fixed in CSS.
The SVG is actually generated by Zint itself, only lightly patched in the wrapper. Zint is a pretty old barcode generator (not meant disrespectfully, quite the opposite actually), it's quite possible that some of its decisions when rendering to SVG are out of date or very conservative. The use of id/global namespace does feel like a potential pain point though, which I will take up with the upstream project.
