JAVASCRIPT ISSUE (i realize this is a java forum not J.S.) URGENT!

Question

Hello,
First off I realize this is a java forum and not Javascript so if you are do not know Javascript ignore this thread. I posted it here because Ive used this before and help is often prompt. However, If anyone out there knows javascript would you be willing to help me real quick on a function issue that i cannot seem to solve? It would be greatly appreciated! I am trying to add a pop up box that displays an error message when they enter the wrong format. For ex. the proper format is 3 letters followed by 3 numbers (INF334). If they enter something such as (INFD334) I want a J.S. pop up box to display and have them try again. I cant seem to figure out where I need to include this within my function I created though. Can someone please help! Here is my function:
function addCourses(arguments) {
  //Declare Variables     
       var class = "-", grade = "-";
       fieldValue = document.InformationForm.CoursesTaken.value;
        if(arguments == null || arguments == '') {
       //Prompt user for input, validate input
         while(!class.match(/[A-Z]{3}[0-9]{3}/) && class != 0 && class != '' && class != null) {
                 class = prompt("Enter a Course ID. Ex. INF110", "");
       else {class = arguments;}
  //Checks for valid Grade Letters including Withdrawals
       while(!grade.match(/[A-DFW]{1}/) && grade != 0 && grade != '' && grade != null && class != '' && class != null && class != 0) {
          grade = prompt(" Enter The Grade Letter Earned. Ex. A B C D F W", "");
       if(class != "" && class != null && grade != '' && grade != null && grade != 0 && class != 0) {
              document.InformationForm.CoursesTaken.value = fieldValue + "" + class + "\t" + grade + "\n";
         newGPA(grade);
         classCount();
}//END addCourses Function

Answer 1

Also, if you don't want to be labeled a loser in this and other forums, please read this:
http://www.catb.org/~esr/faqs/smart-questions.html
especially these sections:
http://www.catb.org/~esr/faqs/smart-questions.html#forum
h2. Choose your forum carefully
Be sensitive in choosing where you ask your question. You are likely to be ignored, or written off as a loser, if you:
post your question to a forum where it's off topic...
http://www.catb.org/~esr/faqs/smart-questions.html#urgent
h2. Don't flag your question as ?Urgent?, even if it is for you
That's your problem, not ours. Claiming urgency is very likely to be counter-productive: most hackers will simply delete such messages as rude and selfish attempts to elicit immediate and special attention.