Smooth scroll to element

scrollToEl.js

function scrollToEl(el) {
  var rect = el.getBoundingClientRect(),
      scrollTop = window.pageYOffset || document.documentElement.scrollTop,
      scrollLeft = window.pageXOffset || document.documentElement.scrollLeft,
      elTop = rect.top + scrollTop,
      elLeft = rect.left + scrollLeft;
  
  window.scrollTo({
    top: elTop,
    left: elLeft,
    behavior: 'smooth'
  });
}