See the example here >>> https://jsfiddle.net/vvup5ob5/3/ or see our work in Lam-v2 (Jun 2018) Link >> http://webtricker.com/projects/lam

Custom parallax effect in a single element.js

// Parallax effect
        if($(".parallax-section").length){
            var winScrollTop=0;
            $.fn.is_on_screen = function(){    
                var win = $(window);
                var viewport = {
                    top : win.scrollTop(),
                    left : win.scrollLeft()
                };
                //viewport.right = viewport.left + win.width();
                viewport.bottom = viewport.top + win.height();

                var bounds = this.offset();
                //bounds.right = bounds.left + this.outerWidth();
                bounds.bottom = bounds.top + this.outerHeight();

                return (!(viewport.bottom < bounds.top || viewport.top > bounds.bottom));
            };

            function parallax() { 
              var scrolled = $(window).scrollTop();
              $('.parallax-section').each(function(){ 

                 if ($(this).is_on_screen()) {	
                            var firstTop = $(this).offset().top; 
                      var $span = $(this).find(".parallax-item");
                      var moveTop = (firstTop-winScrollTop) * 0.0815 //speed;
                      $span.css("transform","translateY("+-moveTop+"px)");
                 }

              });
            }

            $(window).scroll(function(e){
              winScrollTop = $(this).scrollTop();
              parallax();
            });

        }