Well, John, try this. Add a new library from the attached template and open it. You'll see 2 members, John & Bill, with birthdays (I made up yours).
If you open Filter, you'll see one called Marked. If you select it, the members disappear, because no members are marked. You could set that filter as a tab, if you'd like; I would, but I didn't.
Then, note the action button on the bar at the top of the list. If you press it, you'll be prompted for a birth month and birth day. If you enter 1 & 1 and press the checkmark, they both disappear, since none has a birthdate of Jan 1.
If you enter 4 & 18, you'll see Bill, cuz that's my birthdate. If you enter 2 & 19, you'll see John, cuz that's your made up birthdate.
If you look at the code, note...
- I created variables for the field names at the top, so you can just change them to match your field names.
- You'll need a Boolean field called Marked?. You could change that name, too, at the top of the script.
- I left a debug statement in there, but commented it out. If you delete the // on the left, it'll run the next time, and you'll see at the bottom of the screen the birthdays of each of the members, as the script loops through them.
- There are other ways to do this; this seemed like the simplest. If you don't like the Boolean and/or filter, the script will change a bit, but it'll have the same basic structure regardless. You could copy the matching members to another library; that would be a bit more complex, but you'd avoid needing either the Boolean or the filter -- just that other library. There are probably other ways to do it.
Let me know how it works for you. It's easy to write crappy code; that's what most programmers usually do (though not me, of course 😊); I tried here to be on my best behavior, so the code would be as readable and understandable as it could be for you. If you ever want to look up anything about JavaScript, start with my wiki page Memento JavaScript Library, maybe note the links at the bottom of that page, then Google for "MDN JavaScript" and surf to the first result. For dates specifically, Google for "MDN JavaScript Date".