how to get attribute in javascript class 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: javascript get attribute

<div id="id_of_the_element" data-attribute_name="foo"></div>

var elem = document.getElementById("id_of_the_element");
var attribute_value = elem.getAttribute("data-attribute_name");

//OR with jquery...
var attribute_value = $('#id_of_the_element').attr('data-attribute_name');
//OR...
var attribute_value = $('#id_of_the_element').data('attribute_name');