function MediaViewer(){
this.dialog = null;
this.mediaContainers = [];

this.elements=[];

this.init=function(){
var elements=document.querySelectorAll("[mv-dialog]");
for(var i=0; i<elements.length;i++){
var func=function(controller){
return function(){
controller.close();
};
};
elements.addEventListener("click", func(this), true);
this.dialog = elements;
this.dialog.style.display="none";
}
this.close();

var elements=document.querySelectorAll("[mv-item]");
for(var i=0; i<elements.length;i++){
var el = elements;
var src="";

if(el.getAttribute("mv-src")){
src=el.getAttribute("mv-src");
}
else if(el.getAttribute("src")){
src=el.getAttribute("src");
}

var contEl={
id:this.elements.length,
src:src,
type: el.getAttribute("mv-item").length > 0 ? el.getAttribute("mv-item") : el.nodeName
};
this.elements[contEl.id] = contEl;

var func=function(controller, id){
return function (){
controller.openDialog(id);
};
};
el.addEventListener("click", func(this, contEl.id), true);
}

var elements=document.querySelectorAll("[mv-container]");
for(var i=0; i<elements.length;i++){
var el = elements;
var cont={
element:el,
type:el.getAttribute("mv-container").length >0 ? el.getAttribute("mv-container") : el.nodeName
}
var func=function(controller){
return function(){
controller.close();
};
};
elements.addEventListener("click", func(this), true);
this.mediaContainers[this.mediaContainers.length] = cont;
}
};

this.close=function(){
var classes = this.dialog.getAttribute("class");
if(!classes){
classes = "";
}
if(classes.length == 0 || classes.match(/mvvisible/)){
classes=classes.replace(/mvvisible/, "");
classes += " mvinvisible";
this.dialog.setAttribute("class", classes);
}
};

this.openDialog=function(id){
this.dialog.style.display="";
for(var i=0;i<this.mediaContainers.length;i++){
var cont=this.mediaContainers;
if(cont.type.toUpperCase() == this.elements[id].type.toUpperCase()){
cont.element.style.display="";
cont.element.setAttribute("src",this.elements[id].src);
}
else{
cont.element.style.display="none";
}
}
var classes = this.dialog.getAttribute("class");
if(!classes){
classes = "";
}
if(!classes.match(/mvvisible/)){
classes=classes.replace(/mvinvisible/, "");
classes += " mvvisible";
this.dialog.setAttribute("class", classes);
}
}
this.init();
}

<div mv-dialog style="display:none">
<img mv-container="img"/>
<video mv-container="video" autoplay mute></video>
</div>
<script type="text/javascript">
new MediaViewer();
</script>

div[mv-dialog]{
position:fixed;
display:flex;
flex-flow: column;
top:0vh;
left:0vh;
width:100%;
height:100%;
background-color:rgba(0,0,0,0.8);
}

img[mv-item], video[mv-item]{
cursor:pointer;
}

div[mv-dialog].mvvisible{
animation-name:animvvisible;
animation-duration:1s;
display:default;
}

@keyframes animvvisible{
0%{opacity:0;transform:scale(0.5);}
90%{transform:scale(1);}
100%{opacity:1;}
}

div[mv-dialog].mvinvisible{
animation-name:animvinvisible;
animation-duration:2s;
height:0;
}

@keyframes animvinvisible{
0%{opacity:1;transform:scale(1);height:100%;}
90%{transform:scale(0.5);}
100%{opacity:0;height:0;}
}

img[mv-container]{
display:block;
margin-left:auto;
margin-right:auto;
margin-top:5vh;
margin-bottom:auto;
max-width:98vw;
max-height:90vh;
vertical-align:middle;
cursor:pointer;
border-radius:5px;
}

video[mv-container]{
display:block;
margin-left:auto;
margin-right:auto;
margin-top:5vh;
margin-bottom:auto;
max-width:98vw;
max-height:90vh;
vertical-align:middle;
cursor:pointer;
}

<img mv-item src="test.jpg">
<button mv-item="img" mv-src="test.jpg">click to open</button>
<img mv-item mv-src="test.jpg" src="test_thumb.jpg">
<button mv-item="video" mv-src="test.mp4">open video</button>