<script type="text/javascript">
            var fileType = prompt("Enter the image file type.");
            function typeCheck(){
              if (fileType == ".jpg" || fileType == ".img" || fileType == ".png"){ //This checks if the file is a jpg OR img OR png
                alert("File type accepted!");
              } else { //This alert is displayed if the file type is anything else
                alert("Wrong file type!");
              }
            }
          </script>