JSFiddle - React, Tailwind, and code Playground

HTML

<button id="change-world-btn">Change World</button>
<hr />
<h4>Elements with target class name:</h4>
Hello <span class="world-name">World!</span><br />
Hello <span class="world-name">World!</span><br />
Hello <span class="world-name">World!</span><br />
<hr />
<h4>Element with different class name:</h4>
Hello <span class="other-class">World!</span><br />

JavaScript

var worlds = new Array ("Pluto!", "Mars!", "Saturn!", "Earth!", "Mercury!");

function newWorld() {
    return worlds[Math.floor(Math.random() * worlds.length)];
}

elements = document.getElementsByTagName('span');

document.getElementById('change-world-btn').onclick = function() {
    world = newWorld();
    for(var i = 0, el; el = elements[i++];) {
        if(el.className == 'world-name') {
            el.innerHTML = world;
        }
    }
};