<!DOCTYPE html>
<html>
<head>
<style>
div {
border: 1px solid black;
margin: 5px;
}
</style>
</head>
<body>
<div id="myDIV">
<p class="child">A p element with class="child" in a div.</p>
<p class="child">Another p element with class="child" in a div.</p>
<p class="child">A third p element with class="child" in a div.</p>
</div>
<p>Click the button to find out how many elements with class "child" there are inside the div element.</p>
<button onclick="myFunction()">Try it</button>
<p><strong>Note:</strong> The getElementsByClassName() method is not supported in Internet Explorer 8 and earlier versions.</p>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myDIV").getElementsByClassName("child");
document.getElementById("demo").innerHTML = x.length;
}
</script>
</body>
</html>