how do i set an id for a div in js code example

Example 1: javascript change element id

var element = document.getElementById("oldID");
element.id = "newID";

Example 2: get id of element javascript

var element = document.getElementsByTagName("div")[0];
var id = element.id;

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;