fastest way to make an image blink — so fast that you didn’t see it

The standard refresh rate for monitors is 60Hz – 60 times per second. This is a hardware limitation – even with perfect software timing, there’s no way to display frames more frequently than that – and humans paying attention to a screen can easily see something that appears for 1/60th of a second.

Your only option is to have the image appear and disappear with every frame (which can be done more precisely than setInterval with requestAnimationFrame – but it’ll still be visible to those watching closely).

// Ensure browser is not busy
setTimeout(() => {
  window.requestAnimationFrame(() => {
    document.body.classList.toggle('blue');
    window.requestAnimationFrame(() => {
      document.body.classList.toggle('blue');
    });
  });
}, 1000);

.blue {
  background-color: blue;
}

It’s not possible for the monitor to display something for a low enough duration that it’s not perceivable.