let draw =
  () {
    case Dom.Canvas.fromDomElement(canvas) {
      Maybe::Just(el) =>
        {
          el
          |> Canvas.setLineWidth(20)
          |> Canvas.setLineJoin(CanvasLineJoin::Round)
          |> Canvas.beginPath()
          |> Canvas.moveTo(20, 20)
          |> Canvas.lineTo(190, 100)
          |> Canvas.lineTo(280, 20)
          |> Canvas.lineTo(280, 150)
          |> Canvas.stroke()
          ""
        }
      Maybe::Nothing =>
        ""
    }
  }
{
  await Timer.timeout(0)
  draw()
}
<canvas as canvas/>