how to get an attribute of a tag in javascript code example

Example 1: javascript get attribute

//HTML
//<div id="elem" data-id="4hJ3s"></div>

var elem = document.getElementById("elem");
elem.getAttribute("data-id"); // "4hJ3s"

Example 2: dom element get attribute

document.getElementById('id1').getAttribute('attribute');

Example 3: get element attribute javascript

var x = document.getElementsByTagName("H1")[0].getAttribute("class");