breakout/startmenu.js

function startmenu() {
  
  GUI.text("Press ENTER to start", Window.dimensions.scale(0.5));
  GUI.text("Press ESCAPE to exit", Window.dimensions.scale(0.5).add([0,-100]));
}

register_gui(startmenu);

var startcontroller = {
  input_enter_pressed() {
    run("breakout.js");
    Player.players[0].uncontrol(startcontroller);
    unregister_gui(startmenu);
  },

  input_escape_pressed() {
    quit();
  },
};

Player.players[0].control(startcontroller);