<div class="first">
<div><h4>Hello</h4></div>
<div><h4>Hi</h4></div>
<div><h4>Say</h4></div>
</div>
document.getElementsByClassName("first").getElementsByTagName("div").onclick = function() {
alert('World')
}
document.getElementsByClassName('first')[0].getElementsByTagName('div')[0]
document.querySelector('.first > div')