.myclass{
background:green;
width:200px;
height:10px;
margin-top:5px;
}
<body style="background:grey">
<div class="myclass" style="display:none">0</div>
<div class="myclass" style="display:none">1</div>
<div class="myclass" style="display:none">2</div>
<div class="myclass" style="display:none">3</div>
<div class="myclass" style="display:none">4</div>
<div class="myclass" style="display:none">5</div>
<button id="btn">click</button>
<button id="btn2">click2</button>
<script src="my_script_js.js"></script>
</body>
var get_elements = document.querySelectorAll('.myclass');
var btn = document.getElementById('btn');
var btn2 = document.getElementById('btn2');
var i=0;
function shows(){
get_elements[i].style.display = 'block';
if(i>=get_elements.length-1){
null;
}else{
i++;
}
}
function hides(){
get_elements[i].style.display = 'none';
if(i<=0){
null;
}else{
i--;
}
}
btn.addEventListener('click',shows,false);
btn2.addEventListener('click',hides,false);