key_press-func-start-game.js

function key_pressed(key)
{
  if (key.key == "ArrowUp")
  {
      console.log("up");
      if (start_time == 0) // Only start if not already started
      {
        start_time = new Date().getTime(); // Store start time
        setInterval(update, 1000 / frames_per_second); // Start looping update function
      }
  }

  ... // All the rest of the function
}