JSFiddle - React, Tailwind, and code Playground

HTML

<header>dfd</header>

JavaScript

$('header').on('click', function(){
	$(this).addClass('ddd');
});

$("header").bind("DOMSubtreeModified", function() {
    if ( $('header').hasClass('ddd') ) {
    	console.log('класс добавлен');
    }
});