I haven’t rewritten this to work in a modern page, but will post a new Content Editor Web Part written for modern pages within a few weeks (hopefully). This will let you load solutions like SPJS Charts in a modern page.
Sorry for the not checking back on this topic earlier. I have verified that I can make it work in a Modern CEWP (the web part I have crated for modern pages), but I need to tweak some small layout issues before I can release it.
I’ll try to get this done during this week / weekend and release a new version of SPJS Charts supporting modern pages (and the Modern CEWP also).