Extend footer to take up the remainder of the viewport

footerExtend.js

var viewportHeight = Math.max(document.documentElement.clientHeight, window.innerHeight || 0);
var footerDistanceFromTop = $('.footer').offset().top;

if (footerDistanceFromTop < viewportHeight) {
  var footerHeight = viewportHeight - footerDistanceFromTop;
  var footerMinHeight = parseInt($('.footer').css('min-height').split('px')[0]);
  
  if (footerHeight > footerMinHeight) {
    $('.footer').css('height', footerHeight + 'px');
  }
}