var Scrollify = function(){
    this.$elements = $('.js-scrollify');
    this.$win = $(window);
    this.winST = 0;
    this.onScroll = function() {
        var _this = this;

        _this
            .$elements
                .each(function() {
                    var $this         = $(this);
                    var value         = $this.data('scrollify-value');
                    var elementOT     = $this.offset().top + _this.winST;
                    var elementHeight = $this.outerHeight();
                    var elementOB     = elementOT + $this.outerHeight();
                    var winHeight     = _this.$win.outerHeight();
                    var winSB         = _this.winST + winHeight;

                    if (winSB > elementOT && _this.winST < elementOB) {
                        var totalScroll = winHeight + elementHeight;
                        var currentScroll = _this.winST - (elementOT - winHeight);

                        switch($this.data('scrollify-animate')) {
                            case 'translatey':
                                $this.css({
                                    'transform': 'translate(0px, -' + (value * (currentScroll / totalScroll)) + 'px)'
                                });

                                break;

                            case 'translatex':
                                $this.css({
                                    'transform': 'translate(' + (value * (currentScroll / totalScroll)) + 'px, 0px)'
                                });

                                break;

                            case 'opacity':
                                $this.css({
                                    'opacity': value * (currentScroll / totalScroll)
                                });

                                break;

                            case 'scale':
                                $this.css({
                                    'transform': 'scale(' + (value * (currentScroll / totalScroll))+ ')'
                                });

                                break;
                        }
                    }
                });
    }
};