クリックカウンター（笑）

open Dom_html
open Graphics_js
let () = (* open_graph "" *)
  Js.Opt.iter
    (CoerceTo.canvas (getElementById "canvas0"))
    Graphics_js.open_canvas
let rec k c =
  clear_graph ();
  moveto 50 50;
  draw_string (string_of_int c);
  loop [Button_down] (fun event -> k (c + 1))
let () = k 0