I need to use data attribute in my html like <div id="userlist" data-user="A.A.M"></div> then I need to alert the data-user I used

var userlist = document.getElementById("userlist");

var show = userlist.getAttribute("data-user");
alert(show);

My question is how to handle many data-user in the html like

<div id="userlist" data-user="A.A.M"></div> <div id="userlist2" data-user="A.A.M2"></div> to alert A.A.M and A.A.M2

Thanks in advance and sorry for my bad English.