Terms stage: the accept checkbox unlocks only once the terms box has been scrolled to the end (or immediately when the text fits without scrolling).

27 lines of JavaScript Raw file Open on GitHub

/* Terms stage: the accept checkbox unlocks only once the terms box has been
 * scrolled to the end (or immediately when the text fits without scrolling). */
'use strict';

(() => {
  const box = document.getElementById('terms-box');
  const accept = document.getElementById('accept-box');
  const hint = document.getElementById('terms-hint');
  if (!box || !accept) return;

  function unlock() {
    accept.disabled = false;
    if (hint) hint.hidden = true;
    box.removeEventListener('scroll', onScroll);
  }

  function atEnd() {
    return box.scrollTop + box.clientHeight >= box.scrollHeight - 4;
  }

  function onScroll() {
    if (atEnd()) unlock();
  }

  if (atEnd()) unlock();               // fits without scrolling
  else box.addEventListener('scroll', onScroll, { passive: true });
})();