function initCanvas(w, h)
  local canvas = document:createElement("canvas")
  canvas.id = "canvas"
  canvas.width = w
  canvas.height = h
  canvas.style.width = canvas.width .. 'px'
  canvas.style.height = canvas.height .. 'px'
  document:getElementsByTagName('body')[0]:appendChild(canvas)
end
initCanvas(300, 300)