Loop through all checkboxes?

Hi,

I need a way to do the following:

When the page loads, I have 20 or so checkboxes that correspond to categories a user is a member of.  A couple checkboxes may be checked indicating a user is a member of that category, or he/she may have none checked, 2 checked or even all of them.

What I want to do is allow the user to join other categories and/or be removed from categories that they are a member of simply by unchecking the checbox and clicking a button that calls a JavaScript function.

Currently I pass in the memberId and the list of categories they are already subscribed to to an" empty" function called saveCategories.  We need a way to know what the user was subscribed to in the event they uncheck those categories we need to do run a DELETE SQL statement and perhaps an INSERT SQL statement as well if the user removes his/herself from category A and joins category D for example.  I am thinking the flow should be:

1. Loop through all the "checkboxes" in this form that have an id that starts with "category".
2. Build a comma delimited list of the values of each checkbox.
3. Compare the newly subscribed categories to the original subscribed list and basically figure if I need to just do an INSERT or an INSERT and a DELETE statement

Step 3 could be done on the server side I suppose.

Any help appreciated at least for 1 and 2, I think I can do 3 on the server side.

function saveCategories(memberId,subscribedIdList) {

}

Best regards,

-ws