Modify existing points/create point on mouse click

[amarshall8]

Hi! I'm trying to use pts to create a seemingly relatively simple project. Essentially, I want to create a rectangle where all four corners can be dragged to any position and then left there. Eventually I want to add grid lines that appear at regularly spaced intervals between the outermost lines on the opposite edges, but that's a future problem.

Essentially, how can I modify existing points on the canvas by clicking and dragging them to new spots? All the library demos show is mouse tracking. I'm quite new to JS so I'm a bit lost.

As a an even more future goal I'd also love to add a feature where the corner nodes of the 4-sided polygon will light up when you're near to them.

Best,
Alec