I am fairly new to javascript...so please bear with me...

I need to build a basic pop-up that will allow users to do the following:

1) Enter Year.....this can be hardcoded (no problem)
2) Enter Week Number.... this may also be hardcoded (e.g. WK01, WK02)
3) Once the above fields are complete, then when the user submits...the textbox should provide the correct Week Date that corresponds to the Year and Week Number.

I would love if someone could point me in the right direction as to how I can accomplish my 3rd step.

Thank you!