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<!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 with id="myDIV".</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> <script> function myFunction() { var x = document.getElementById("myDIV"); var y = x.getElementsByClassName("child"); var i; for (i = 0; i < y.length; i++) { y[i].style.backgroundColor = "red"; } } </script> </body> </html>