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1. #THINGS HAPPEN THAT LEAVE A MARK IN SPACE IN TIME IN US CODE#
2. #THINGS HAPPEN THAT LEAVE A MARK IN SPACE IN TIME IN US FREE#

Keep reading for a more detailed explanation about intersection observer options. To watch for intersection relative to the device's viewport, specify null for root option. Typically, you'll want to watch for intersection changes with regard to the target element's closest scrollable ancestor, or, if the target element isn't a descendant of a scrollable element, the device's viewport.

That specified element is called the root element or root for the purposes of the Intersection Observer API.

#THINGS HAPPEN THAT LEAVE A MARK IN SPACE IN TIME IN US FREE#

This way, sites no longer need to do anything on the main thread to watch for this kind of element intersection, and the browser is free to optimize the management of intersections as it sees fit.

#THINGS HAPPEN THAT LEAVE A MARK IN SPACE IN TIME IN US CODE#

The Intersection Observer API lets code register a callback function that is executed whenever an element they wish to monitor enters or exits another element (or the viewport), or when the amount by which the two intersect changes by a requested amount. As the user scrolls the page, these intersection detection routines are firing constantly during the scroll handling code, resulting in an experience that leaves the user frustrated with the browser, the website, and their computer. The author of the website may not even realize this is happening, since they may know very little about the inner workings of the two libraries they are using. Each of these has its own intersection detection routines, all running on the main thread. It uses a vendor-provided library to manage the advertisements placed periodically throughout the page, has animated graphics here and there, and uses a custom library that draws notification boxes and the like. When a site is loaded with these tests, things can get downright ugly.Ĭonsider a web page that uses infinite scrolling. Since all this code runs on the main thread, even one of these can cause performance problems. Implementing intersection detection in the past involved event handlers and loops calling methods like Element.getBoundingClientRect() to build up the needed information for every element affected. Deciding whether or not to perform tasks or animation processes based on whether or not the user will see the result.Reporting of visibility of advertisements in order to calculate ad revenues.Implementing "infinite scrolling" websites, where more and more content is loaded and rendered as you scroll, so that the user doesn't have to flip through pages.

Lazy-loading of images or other content as a page is scrolled.Intersection information is needed for many reasons, such as:

As the web has matured, the need for this kind of information has grown. Historically, detecting visibility of an element, or the relative visibility of two elements in relation to each other, has been a difficult task for which solutions have been unreliable and prone to causing the browser and the sites the user is accessing to become sluggish. The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport.