Finding all class names used in HTML/DOM

Answer 1

Get all the classes & the unique ones in one dimension.

const allClasses = Array.from(new Set(document.querySelectorAll("*").map(el => el.classNames)));

const flatClasses = Array.from(new Set(allClasses.flat(1)))

Answer 2

This is HTML:

<div id="oye">
<div class="pop"></div>
<div class="hop"></div>
<div class="bob"></div>
</div>

<p id="my"></p>

In Jquery, You will get array of all class name, Check below code

 $(document).ready(function(){
  var myclass = [];
  var parent = $("#oye");
    var divs = parent.children();

  for(var i = 0; i < divs.length; i++){

    myclass.push(divs[i].className)
  }

  //console.log(myclass);


  var myclasses = myclass.join(', ');

  $("#my").html(myclasses);


});

See Demo Here: https://codepen.io/ihemant360/pen/PzWJZP