Smooth scroll to a specified DOM element

scroll-to-element.js

// based on https://gist.github.com/andjosh/6764939
function scrollToElem(target, duration) {
  var start = window.pageYOffset;
  var to = target.getBoundingClientRect().top;
  var change = to - start;
  var currentTime = 0;
  var increment = 20;

  function animateScroll(){
    currentTime += increment;
    var val = easeInOutQuad(currentTime, start, change, duration);
    window.scrollTo(window.pageXOffset, val);
    if (currentTime < duration) {
        setTimeout(animateScroll, increment);
    }
  };
  animateScroll();

  //t = current time
  //b = start value
  //c = change in value
  //d = duration
  function easeInOutQuad(t, b, c, d) {
    t /= d/2;
    if (t < 1) return c/2*t*t + b;
    t--;
    return -c/2 * (t*(t-2) - 1) + b;
  };
}