How to configure IntersectionObserver?

The page is divided into several sections. You need to colback worked only when crossing a section of the top border of the viewport. Is it possible to achieve this using IntersectionObserver?
June 3rd 19 at 19:06
2 answers
June 3rd 19 at 19:08
if ('IntersectionObserver' in window) {

 let config = { 
 root: document.querySelector('#scrollArea'), // if not specified, root is the viewport
 rootMargin: '0px', // '10px 10px 10px 10px' margins will be included in the tracking area of intersection. The Observer will call for kalbak 10px to the intersection of the section c either side root. 'px' is mandatory.
 threshold: [.0,.1,.2,.3,.4,.5,.6,.7,.8,.9,1] // call, kalbac crossing every 10%. [0] to call kulbaka once at the first intersection

 // set up observer handler and config
 sectionObserver = new IntersectionObserver(onIntersection, config); 

 // bind the created observer on elements 
 let sections = document.querySelectorAll('section');
 sections.forEach(section => {

 // handler observer
 onIntersection function (entries, self) {
 if (entry.intersectionRatio > 0.5) {
 // section crossed observer's root 50%
Thank you! - Tanner_Murazik commented on June 3rd 19 at 19:11
June 3rd 19 at 19:10
The "correct" method I found, but you can check, when crossing the upper boundary it is near zero, and at the intersection of the bottom is approximately equal to the height of the viewport.

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