原生JS图片懒加载

加载条件

img.offsetTop < window.innerHeight + document.body.scrollTop;

代码

  var imgs = document.querySelectorAll('img');
      window.onscroll = function(){
          var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
          var winTop = window.innerHeight;
          for(var i=0;i < imgs.length;i++){
              if(imgs[i].offsetTop < scrollTop + winTop ){
                  imgs[i].src = imgs[i].getAttribute('data-src');
              }
          }
      }