​​What is Intersection Observer & How to implement it

What is Intersection Observer, It gives a smooth scrolling, experience to the user, Lazy-loading of images or other elements as the page is scrolled, ​ Optimize bandwidth usage. In simple words it keeps noting if the position of your selected DOM element is in the viewport while scrolling, when your selected DOM element touches the bottom of page while scrolling you can make a method get triggered (i.e., callback)