intersectionObserver.html

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style>
			#box{
				width: 200px;
				height: 100px;
				background-color: red;
				position: absolute;
				top: 2300px;
				left: 0;
			}
			body{
				height: 4000px;
			}
		</style>
	</head>
	<body>
		<div id="box"></div>
		<script type="text/javascript">
			var
				ele = document.getElementById("box"),
				ob = new IntersectionObserver(
					changes => {
						for(const change of changes) {
							// Timestamp when the change occurred
							console.log(change.time);  
							// Unclipped area of root
						    console.log(change.rootBounds);
						    // target.boundingClientRect()
						    console.log(change.boundingClientRect); 
						    // boundingClientRect, clipped by its containing block ancestors, and intersected with rootBounds
						    console.log(change.intersectionRect); 
						    // Ratio of intersectionRect area to boundingClientRect area
						    console.log(change.intersectionRatio);
						    // the Element target
						    console.log(change.target);             
						}
					},
					{
						threshold: [1],
						root: document.querySelector('body'),
						rootMargin: "100px"
					}
				);
			//共触发两次，进入可视区和离开可视区
			ob.observe(ele);
			var a = ob.takeRecords();
			console.dir(a);
		</script>
	</body>
</html>