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<!DOCTYPE html> <html> <head> <style> .mystyle { width: 500px; height: 50px; border: 1px solid black; } .anotherClass { background-color: lightblue; padding: 25px; } .thirdClass { text-align: center; font-size: 25px; color: navy; margin-bottom: 10px; } </style> </head> <body> <p>Click the button to find out if the DIV element has a class of "mystyle". If so, remove "anotherClass".</p> <div id="myDIV" class="mystyle anotherClass thirdClass"> I am a DIV element </div> <button onclick="myFunction()">Try it</button> <p><strong>Note:</strong> The classList property is not supported in Internet Explorer 9 and earlier versions.</p> <script> function myFunction() { var x = document.getElementById("myDIV"); if (x.classList.contains("mystyle")) { x.classList.remove("anotherClass"); } else { alert("Could not find it."); } } </script> </body> </html>