JSFiddle - React, Tailwind, and code Playground

HTML

<div class="test">Test</div>
	<div class="test2">One more</div>

CSS

.newClass {
    color: red
}

JavaScript

var $ = function(selectors) {
	return document.querySelectorAll(selectors);
}

Node.prototype.addClass = function (param) {
	var myNodeList = this;
	this.className = this.className + " " + param;
	return this;
}

NodeList.prototype.each = function (callback) {
	var myNodeList = this;
	for (var i = 0; i < myNodeList.length; i++) {
        console.log(myNodeList[i] instanceof Node);
		callback.call(myNodeList[i]);
	}
	return this;
}
console.log($(".test").each(function () {
    
    this.addClass('newClass')
}));