You should see some of the content that first-time creators are making. Take this simple sketchpad app on the web for example: cheap, simple, good for what little it does. This is a great job for a newcomer to the community, but of course, the best part is seeing what can be improved. For starters, there doesn't seem to be a way to revert back into pen mode from the eraser, but maybe that's just Chrome being a disagreeable old bat on my setup.
On the less obvious and more technical end of the spectrum, it appears that the creator hasn't taken mobile access into account. You basically access the site and, well, do nothing whatsoever; the site thinks you're trying to scroll instead of performing brush strokes. This is sort of important to think about seeing as more people will access the web from an Android or iPhone handset today whereas a PC is probably what this site was made from; ergo, it was probably created from scratch to run on that platform alone. Credit is given where it's due, and I suppose it's a passable effort despite this trip-up.
Setting that little caveat aside, the drawing function is rather primitive and not terribly smooth as a result; a dose of canvas.addEventListener('mousemove', draw) could help, but what he really needs is window.requestAnimationFrame(draw). The problem with the mousemove command is that it skips frames whereas requestAnimationFrame is more consistent and reliable in this fashion. Come think of it, setInterval would be a great idea for smooth strokes at high speed too. Oh, so much room for improvement.
One other point: Using div for precise positioning of interactable page elements is what you'd call a markup nightmare. Few developers actually use this command very often for this specific function, and it's thanks to how difficult it can be to get the elements exactly where they can play nice with whatever aspect ratio the display window is set to. Besides that, there's not much left for criticism, but it's worth noting that the creator could get some serious practice by weaving a multiuser command into the mix. For more information click here http://sketchy.gq/.