Loop through all elements with class="child" in a <div> element, and change their background color.
Click the button to add a background color to all elements with class="child" inside the div element.
<!DOCTYPE html> <html> <head> <style> div {//from ww w . ja v a2 s.co m 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> <button onclick="myFunction()">Test</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>