Just finished my d3 scatterplot project.
Thanks in advance for any feedback 
Hello Nathan,
Wonderful progress comrade, you are the good dev, perfect work.
Just checked you work, and so happy you could apply the great updates and fix very good.
The only issue I can think about is being responsive.
I suggest as you take the width and height as constant values, you may think about get the minimum of the screen and the default values, for example
const h = min(600,<<screen_heigh>>);
const w = min(1000,<<screen_width>>);
One good practice also could be listening to windows resize event, and redraw the chart(if required). but remember cache the external JSON data somewhere to not call it over and over becasue of too much draw functions.
Maybe think about a filtered(zoomed) result too!
One small improvement you can do is about two overlapped dots on graph. For example considering following:
For checking the data of that green dot behind the red, user should hover the mouse pointer very precious in away on green dot only, and it’s hard. Sometimes some dots are completely masked by another dot, no chance to have their data.
I suggest when you hover on a dot, you check and show any other masked dot by mouse pointer.
Overall looks good Nathan, very good work.
Keep working on great work, happy coding.
Thanks @NULL_dev great feedback as always