JS 的 background url()
html - Cache images fetched via background-url CSS property - Stack Overflow
background url() 带缓存，不会重复的往后台请求
强缓存
Cache-Control
Pragma
html - Cache images fetched via background-url CSS property - Stack Overflow
background url() 带缓存，不会重复的往后台请求
Cache-Control
Pragma