<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="container">
<div class="row">
<div class="bye-world">·</div>
<div class="hello-world">·</div>
<input class="btn toggler" type="button" value="Toggle" />
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.17.0/TweenMax.min.js"></script>
<script>
var byeWorld=document.querySelectorAll('.bye-world')[0];
var helloWorld=document.querySelectorAll('.hello-world')[0];
var toggleButton=document.querySelectorAll('.toggler')[0];
var timeline=new TimelineMax({paused:true,reversed:true});
var duration=.8;
function init(){
toggleButton.addEventListener('click',swap,false);
TweenMax.set(helloWorld,{opacity:0});
timeline.to(byeWorld,duration,{opacity:0,ease:Power2.easeIn}).to(helloWorld,duration,{opacity:1,ease:Power2.easeOut});
}
function swap(){
(timeline.reversed())?timeline.play():timeline.reverse();
}
