How make a validator for a parent function?

Im making a web site which encrypt texts and decrypt them, already I managed asignning the funcionalities to the buttons and enclose this functions into a parent function with the finality that the user only can use the web site after do click in “aceppt thte terms of use” (with a checkbox), so all good at this point beacuse I bond this button as well but I found that after the first click in the button dosent matter if this isnt mark anymore the parent function dont “return”.

I wanna make a validator for this checkbox.

Well my first thought was made another parent function bellow all like this:

document.getElementId("MycheckboxButton").addEeventListener("change", validator);

function validator() {
  const terms = document.getElementId("MycheckboxButton").value
  if (check.checked) {}

But to be short i dont know exactly how do it wel… Can you help me please guys 🙂