let draw =
  () {
    case Dom.Canvas.fromDomElement(canvas) {
      Maybe::Just(el) =>
        {
          // Create path
          let region =
            Path2D.create()
          region
          |> Path2D.moveTo(30, 90)
          |> Path2D.lineTo(110, 20)
          |> Path2D.lineTo(240, 130)
          |> Path2D.lineTo(60, 130)
          |> Path2D.lineTo(190, 20)
          |> Path2D.lineTo(270, 90)
          |> Path2D.closePath()
          // Fill path
          el
          |> Canvas.setFillStyle(CanvasFillStyle::String("green"))
          |> Canvas.fillPath(region, CanvasFillRule::EvenOdd)
          ""
        }
      Maybe::Nothing =>
        ""
    }
  }
{
  await Timer.timeout(0)
  draw()
}
<canvas as canvas/>