Hi Stas,
Also, I suspect this engine does not implement path queries right
It doesn't implement them at all; it reads the first predicate and ignores the rest.
Right now, the engine implements: – BGPs – UNION – OPTIONAL – some FILTERs (https://github.com/LinkedDataFragments/Client.js/blob/master/lib/util/Sparql...)
Or, very simply put: everything needed to run the common SemWeb benchmarks such as BSBM, WatDiv, FedBench.
That's all we can afford as researchers, unfortunately :-) I hope to build more (and lots was built in my spare time), but my currency as a researcher is publishable results, and sadly, not many SPARQL features are.
Nonetheless, plenty of things to have fun with, and I'm happy to put feature requests on the list.
Best,
Ruben
PS There are plans for a new open-source SPARQL/JS engine powered by a larger development team, but that will take its time.