let draw =
  () {
    case Dom.Canvas.fromDomElement(canvas) {
      Maybe::Just(el) =>
        {
          let dims =
            el
            |> Dom.Canvas.toDomElement
            |> Dom.getDimensions
          // Create circular clipping region
          el
          |> Canvas.beginPath
          |> Canvas.arc(100, 75, 50, 0, `Math.PI` * 2)
          |> Canvas.clip
          // Draw stuff that gets clipped
          el
          |> Canvas.setFillStyle(CanvasFillStyle::String("blue"))
          |> Canvas.fillRect(0, 0, dims.width, dims.height)
          |> Canvas.setFillStyle(CanvasFillStyle::String("orange"))
          |> Canvas.fillRect(0, 0, 100, 100)
          ""
        }
      Maybe::Nothing =>
        ""
    }
  }
{
  await Timer.timeout(0)
  draw()
}
<canvas as canvas/>