JSFiddle - React, Tailwind, and code Playground

HTML

<p class="foo">foo</p>
<p class="bar">bar</p>
<p class="foo">foo</p>
<p class="foo">foo</p>
<p class="bar">bar</p>
<p class="bar">bar</p>

JavaScript

var retrieve = function(className) {
    return document.getElementsByClassName(className);
};

var elements = retrieve('foo');

for (var i = 0; i < elements.length; i++)
    elements[i].style.background = '#dfd';