Get unique links in viewport of a page

unique-viewport-links.js

function isAnyPartOfElementInViewport(el) {
  const rect = el.getBoundingClientRect();
  const windowHeight = (window.innerHeight || document.documentElement.clientHeight);
  const windowWidth = (window.innerWidth || document.documentElement.clientWidth);

  const vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
  const horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);

  return (vertInView && horInView);
}

function unique(propertyName) {
  return ((e, i, array) => array.findIndex(a => a[propertyName] === e[propertyName]) === i);
}


console.log(Array.from(document.querySelectorAll('a[href]')).filter(isAnyPartOfElementInViewport).filter(unique('href')).length)