Ensures the highest the footer will ever be on the screen is the bottom of the viewport

stickyFooter.js

// Ensures the highest the footer will ever be on the screen is the bottom of the viewport
var stickyFooter = function () {
  var footer = document.querySelector('footer')

  if (window.innerHeight > document.body.scrollHeight) {
    footer.style.bottom = 0
    footer.style.left = 0
    footer.style.position = 'fixed'
    footer.style.right = 0
  } else {
    footer.style.bottom = null
    footer.style.left = null
    footer.style.position = null
    footer.style.right = null
  }
}

window.addEventListener('load', stickyFooter);
window.addEventListener('resize', stickyFooter);