As a learning activity, the D3 scatter plot is a fine project, but I wonder if it could be better by replacing the dataset.
Given the nature of the dataset (bicycle racing times that often differ by small fractions of time), it is difficult or practically impossible to hover over some of the marks because they overlap so much that it would take enormous svg dimensions to display them far apart enough to be able to hover. See screenshot or Codepen below.
https://www.screencast.com/t/vDHzRM3XOS
https://codepen.io/dr_rompecabezas/pen/WNpROrp
I also wonder whether it would be best to use a dataset that better exemplifies the use of a scatterplot from a data analysis perspective. Without the hovering functionality, it would seem from looking at the graph that the practice of doping has been dropping over time in correlation with race times. However, the dataset is so tiny (just 35 data points), that I would be reluctant to draw too many conclusions.
My two cents. Other than that, I must say I’m loving the curriculum and the freeCodeCamp project. Keep up the great work.