反向查找，截取字符串
=IFERROR(MID(M7,FIND("+",SUBSTITUTE(M7,"\","+",LEN(M7)-LEN(SUBSTITUTE(M7,"\",""))))+1,FIND(".js",M7)-FIND("+",SUBSTITUTE(M7,"\","+",LEN(M7)-LEN(SUBSTITUTE(M7,"\",""))))-1),"")
