const options = { root: document.getElementById('some-id'), // leave blank for viewport rootMargin: '0px', threshold: 1.0, }; const observer = new IntersectionObserver(observeTestamonialInViewPortCB, options); const observeTestamonialInViewPortCB = (entries, observer) => { entries.forEach((entry) => { log(entry); // to stop observer: observer.unobserve(); }); }; const target = document.getElementById('target-element'); observer.observe(target);