Some entries appear empty because they only have an "unstructured" key. Might be useful to handle all three cases:
1. DOI
2. author + year + volume-title
3. unstructured
The output here breaks for https://doi.org/10.1016/S0925-7721(98)00035-2 . It's possible that the structure of a data entry depends on the source ("CrossRef" in this case). I haven't found a spec yet.
Keep in mind that I'm not the author of citation-js, I just created this notebook to look into it and published it since it might be interesting for others... but feedback is very welcome of course ; )