js create div with id code example

Example 1: create element javascript with id

var btn = document.createElement('div'); 
btn.setAttribute("id", "div1");

Example 2: js create element with class

var element =document.createElement("span");
        element.className = "aClassName";

Example 3: how do i set an id for a div in js

All currently used browsers:
element.id=id;
myElement.id=newId;

element.className=class;
myElement.className=newClassName;