I understand the basics… BUT. 
I actually really like this lesson, but the resources at d3js.org, seem to be mostly outdated. I find myself going back and forth the documentation, release notes, and tutorials(outdated). And I feel really stuck atm. And, not like functional JS stuck. Like, stuck stuck, a looping endless loop. 
Barchart? Sure… Scatterplot? Sure… Heatmap… Umm,erm, 
I think I’ll skip for now. Your thoughts please… 