Check If an Element is Visible in the Viewport

isInViewport.js

/* 
  If the element is in the viewport, the function returns true. Otherwise, it returns false.
  https://www.javascripttutorial.net/dom/css/check-if-an-element-is-visible-in-the-viewport/
*/

function isInViewport(el) {
    const rect = el.getBoundingClientRect();
    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
        rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );
}