let loading = document.getElementByid("#id");
let isLoading = false;
let obser = new IntersectionObserver(function(value) {
let value = value[0];
if (value.isIntersecting && !isLoading) {
// 进行加载
}
},{
thresholds: 0.3 //重叠30%面积时
});
// 例子
obser.observe(loading);