jQuery(document).ready(function($){
  	var timelineBlocks = $('.cd-timeline-block'),
  		offset = 0.8;
  
  	//hide timeline blocks which are outside the viewport
  	hideBlocks(timelineBlocks, offset);
  
  	//on scolling, show/animate timeline blocks when enter the viewport
  	$(window).on('scroll', function(){
  		(!window.requestAnimationFrame) 
  			? setTimeout(function(){ showBlocks(timelineBlocks, offset); }, 100)
  			: window.requestAnimationFrame(function(){ showBlocks(timelineBlocks, offset); });
  	});
  
  	function hideBlocks(blocks, offset) {
  		blocks.each(function(){
  			( $(this).offset().top > $(window).scrollTop()+$(window).height()*offset ) && $(this).find('.cd-timeline-img, .cd-timeline-content').addClass('is-hidden');
  		});
  	}
  
  	function showBlocks(blocks, offset) {
  		blocks.each(function(){
  			( $(this).offset().top <= $(window).scrollTop()+$(window).height()*offset && $(this).find('.cd-timeline-img').hasClass('is-hidden') ) && $(this).find('.cd-timeline-img, .cd-timeline-content').removeClass('is-hidden').addClass('bounce-in');
  		});
  	}
  });