Native JavaScript smooth scrolling to internal anchors

smoothscrolling.js

var smoothScrolling = {
  // add smooth vertical scrolling to internal anchors
  init: function() {
    // if new native support available we don't need any of this
    var isSmoothScrollSupported = 'scrollBehavior' in document.documentElement.style;
    if (isSmoothScrollSupported) {
      return;
    }

    this.bindEvents();
  },

  bindEvents: function() {
    window.addEventListener('click', this.triggerScroll.bind(this), false);
  },

  triggerScroll: function(event) {
    // is this an internal anchor?
    if (event.target.hash && event.target.pathname.replace(/^\//, '') === location.pathname.replace(/^\//, '')) {
      var target = document.getElementById(event.target.hash.slice(1)),
        targetY = this.getElementY(target);
      this.smoothScroll(targetY);
    }
  },

  getElementY: function(element) {
    var y = element.offsetTop,
      node = element;
    while (node.offsetParent && node.offsetParent !== document.body) {
      node = node.offsetParent;
      y += node.offsetTop;
    }
    return y;
  },

  getCurrentY: function() {
    // Firefox, Chrome, Opera, Safari
    if (window.self.pageYOffset) {
      return window.self.pageYOffset;
    }
    // Internet Explorer 6 - standards mode
    if (document.documentElement && document.documentElement.scrollTop) {
      return document.documentElement.scrollTop;
    }
    // Internet Explorer 6, 7 and 8
    if (document.body.scrollTop) {
      return document.body.scrollTop;
    }
    return 0;
  },

  smoothScroll: function(targetY) {
    var startY = this.getCurrentY(),
      scrollBy = targetY - startY,
      speed = Math.abs(scrollBy / 100),
      increment = scrollBy / 25;

    // if close just jump
    if (Math.abs(scrollBy) < 100) {
      scrollTo(0, targetY);
      return;
    }
    // otherwise animate the scroll
    var intermediateY;
    for (var i = 0; i <= 25; i++) {
      intermediateY = Math.round(startY + i * increment);
      setTimeout("window.scrollTo(0, " + intermediateY + ")", Math.round(i * speed));
    }
  }
};
smoothScrolling.init();