Tryit Editor v2.9

Edit This Code:
<!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>A p element in div with a <span class="child">span element with class="child"</span> inside of it.</p>
</div>

<p>Click the button to add a background color to all elements with class="child" inside the div element.</p>

<button onclick="myFunction()">Try it</button>

<script>
function myFunction() {
    var div = document.getElementById("myDIV");
    var nodelist = div.getElementsByClassName("child");
    
    var i;
    for (i = 0; i < nodelist.length; i++) {
        nodelist[i].style.backgroundColor = "red";
    }
}
</script>

</body>
</html>