Better performance and simpler lazy loading of intersectionobserverentry (observer)

（ The following are personal understandings used in the project , If you have any mistakes, please correct them ）
IntersectionObserverEntry It is used to observe the interaction degree of two nodes

One 、 Get the observed node

Triggered when the observed node enters the visual interface

var target = document.getElementById('xxx')

Two 、 Create observers

var loadingObserver = new IntersectionObserver(ObserverList=>{
		// ObserverList Is an array of observed nodes , Of each of these elements isIntersecting Represents entry or exit 
        if(ObserverList[0].isIntersecting){
        	console.log(' Being loaded ...')
        }
    },{
    	//  The degree to which the two goals overlap 
        threshold: 0.1,
        // root  by null Or when not writing, it defaults to the browser visual interface 
        root: null
    })

3、 ... and 、 Add the observed target

	// target  Will be inserted   above ObserverList  in 
	loadingObserver.observe(target)

	//  Multiple can be added 
	loadingObserver.observe(target1)
	loadingObserver.observe(target2)