What is lazy loading and pre-loaded?
A little complicated way of saying reference: https://www.cnblogs.com/zhonghuali/p/9625943.html
My personal understanding is: pre-loaded in advance to download pictures and other resources to the client, a one-time request to all the resources required from the client calls when rendering, reducing the number of http requests, optimize performance, but will increase the pressure on the server (once All Image caching), the performance is when you open the page, the picture becomes clear fuzzy.
When lazy loading is give img reserved position, but does not directly load the picture information, such as browsing to a designated area to display the picture designated area, to reduce the burden on the server, and faster page loads. (Page for the browser to request no part of the picture information such as Jingdong, Taobao search results page product list).