jquery centerify

centerify.js

jQuery(document).ready(function ($) {

    ;(function() {
        function Centerify(elem, options) {
            var self = this;

            self.$elem = $(elem);
            self.$sections = self.$elem.children('section');
            self.isAnimating = false;
            self.bodyAndHeadEl = $('body');
            self.count = self.$sections.length;
            self.speed = 100;
            self.wait = 500;

            init();

            function init() {
                onResize();
            }

            function onResize() {
                self.windowHeight = $(window).height();
            }

            function centerOnSegment(percentage) {
                if (!percentage) {
                    return;
                }

                if (self.isAnimating) {
                    return;
                }

                var done = function done() {
                    self.isAnimating = false;
                    $(window).off('scroll', scrollEvent);
                    $(window).unbind('scroll mousedown wheel DOMMouseScroll mousewheel keyup', scrollEvent);

                    if (self.bodyAndHeadEl.get(0).scrollTop === 0) {
                        return;
                    }
                };

                var scrollEvent = function scrollEvent(e) {
                    if (e.which > 0 || e.type == 'mousedown' || e.type == 'mousewheel') {
                        self.bodyAndHeadEl.stop();
                        done();
                    }
                };

                $(window).bind('scroll mousedown wheel DOMMouseScroll mousewheel keyup', scrollEvent);

                clearTimeout(self.onScrollTimer);

                self.isAnimating = true;

                self.bodyAndHeadEl.stop().animate({
                    scrollTop: (Math.round(percentage) * self.windowHeight)
                }, self.speed, function () {
                    return done();
                });
            }

            $(window).bind('scroll', function() {
                clearTimeout(self.onScrollTimer);

                self.onScrollTimer = setTimeout(function () {
                    var currentScroll =  self.bodyAndHeadEl.scrollTop();
                    var currentPercentage = (currentScroll / self.windowHeight).toFixed(2);
                    centerOnSegment(currentPercentage);
                }, self.wait);
            });
        }

        $.fn.centerify = function(options) {
            return this.each(function() {
                if (!$(this).data('centerify'))
                    $(this).data('centerify', new Centerify(this, options));
            });
        };
    })();

    $('#index').centerify();

});