let draw =
  () {
    case Dom.Canvas.fromDomElement(canvas) {
      Maybe::Just(el) =>
        {
          // Add five color stops
          let gradient =
            Canvas.createLinearGradient(el, 20, 0, 220, 0)
            |> CanvasGradient.addColorStop(0, "green")
            |> CanvasGradient.addColorStop(0.5, "cyan")
            |> CanvasGradient.addColorStop(1, "green")
          // Set the fill style and draw a rectangle
          el
          |> Canvas.setFillStyle(CanvasFillStyle::Gradient(gradient))
          |> Canvas.fillRect(20, 20, 200, 200)
          ""
        }
      Maybe::Nothing =>
        ""
    }
  }
{
  await Timer.timeout(0)
  draw()
}
<canvas as canvas/>