code: function drawLoop () {
    ctx.clearRect(0, 0, canvas.width, canvas.height)
  
    var centerX = canvas.width / 2
    var centerY = canvas.height / 2
  
    // draw circle
    ctx.beginPath()
    ctx.arc(centerX, centerY, 100, 0, 2 * Math.PI, false)
    ctx.fillStyle = 'yellow'
    ctx.fill()
  
    // draw three oscilloscopes in different positions and colors
    ctx.strokeStyle = 'lime'
    scope.draw(ctx, 0, 0, centerX, centerY)
  
    ctx.strokeStyle = 'cyan'
    scope.draw(ctx, centerX, 0, centerX, centerY)
  
    ctx.strokeStyle = 'red'
    scope.draw(ctx, 0, centerY, null, centerY)
  
    window.requestAnimationFrame(drawLoop)
  }
docs: custom animation loop