is possible we need js experience
user.js:
var list = "html code here"
document.getElemetById("userlist").innerHTML = list;
mysite.com/index.html:
<div id="userlist"></div> <script src="/user.js"></script>
file js -userlister
header code:
var list = "
code:
html here
footer code:
"
document.getElementById("userlist").innerHTML = list;