Exit from fullscreen mode on click in JavaScript

const exitBtn = document.getElementById('exit-btn');

exitBtn.addEventListener('click', ()=>{
    if (document.fullscreenElement) {
        document.exitFullscreen();
    }
});

To exit from a full-screen mode using vanilla JavaScript use the exitFullscreen method. The Document method exitFullscreen() requests that the element on this document which is currently being presented in full-screen mode be taken out of full-screen mode, restoring the previous state of the screen.

Before calling exitFullscreen check if there is any element in full-screen mode to avoid errors using if (document.fullscreenElement)

Also, note that you need to call exitFullscreen on the document and not on the element .