js正则替换标签

Question

let str='<i>dddd</i><i style="background:red">aaaaa</i><i>tttt</i>'
let str2='<i>dddd</i>aaaaa<i>tttt</i>'
怎么将str替换成str2那样的,'<i style="background:red">aaaaa</i>';中间的值aaa是变动的,但'<i style="background:red">'这个字符是固定的

Answer 1

str='<i>dddd</i><i style="background:red">aaaaa</i><i>tttt</i>'
str.replace(/<i style="background:red">([a-z0-9]*)<\/i>/,'$1')

Answer 2

let str2='<i>dddd</i>aaaaa<i>tttt</i>'
let str = str2.replace(/<\/i>(.*?)<i>/, "$'<i style=\"background:red\">$1</i>$`")