Great point, and I think this is a next step for me. For what it's worth, this was to teach myself React and Redux and took a couple of nights of work. I was curious about ways to keep the canvas element fundamentally decoupled from the algorithm itself, which allows a couple of benefits out of the box. For example, varying the randomness or changing the color map mid-calculation, I kind of got 'for free', thanks to React re-rendering the canvas every time the algorithm is stepped through or the controls are changed.

It's also worth noting that the algorithm's speed here is tied to (I believe?) your monitor's refresh rate, since it's using requestAnimationFrame to loop without blocking the main thread entirely. I'd briefly considered a "complete" button which would run the whole thing in one go and render once, and that would enable reviewing for performance optimisation without hanging the page. But... I got too excited and wanted to share it first.

It's kinda flawed in that it produces terrain with prominent creases along the x/y axis. Most terrain generators use something with less artifacts, like several passes of perlin noise.

Effectively, yes. It's a multiplier for the random displacement that's calculated for a point in the grid as part of the algorithm, which is added to the mean of the adjacent (diamond- or square-wise) points.