Returns whether the element is visible in the viewport

in viewport

function isElementInViewport(el) {
    var rect = el.getBoundingClientRect();

    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document. documentElement.clientHeight) && /*or $(window).height() */
        rect.right <= (window.innerWidth || document. documentElement.clientWidth) /*or $(window).width() */
        );
}