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<!DOCTYPE html> <html> <body> <form> First Name: <input type="text" id="fname" value="Donald"> <br><br> Convert to upper case <input type="checkbox" onclick="if(this.checked){myFunction()}"> </form> <script> function myFunction() { document.getElementById("fname").value = document.getElementById("fname").value.toUpperCase(); } </script> </body> </html>