JSFiddle - React, Tailwind, and code Playground

HTML

<div class="foo"></div>
<div class="foo baz"></div>
<div class="bar"></div>

JavaScript

$(function(){

    var result = [];    
    
    $('*').each(function(k, v){
    
        var classNames = $(v).prop('class');

        if(classNames){
            
            var classes = classNames.split(' ');
            
            $.each(classes, function(k2, v2){
                
                if($.inArray(v2, result) === -1)
                    result.push(v2);
            });
        }
            
    });
    
    console.log(result);

});