javascript html getelementbyid var modalpopup

Pop up doesn't show me the photo I want

Problem with 'Classes' and GetElementById?

As you can see in my CodePen, there are some photo in the Gallery section, when you click on someone of that, there is a pop up shows up, i need to open each different photo in that pop up when you click on that, and some info about the product, near the photo on the pop up, I think there is a problem in the Var on JS, I have to name the classes of the photo from child 1 to child 15?

I don't understand where the problem is

window.onload=function(){

  var selectable = document.getElementsByClassName('child');
  for(var i = 0, j = selectable.length; i < j; i++) {
    selectable[i].addEventListener("click", function() {
  	document.querySelector('.bg-modal').style.display = "flex";
  });
  }


  document.querySelector('.close').addEventListener("click", function() {
  	document.querySelector('.bg-modal').style.display = "none";
  });


}

@import url('https://fonts.googleapis.com/css?family=IBM+Plex+Mono');




body {
  font-family: 'IBM Plex Mono', monospace;
  background-color: #000000;
height: 100%;

}

.header{
	height: 100vh;
  color: #f1f1f1;
	display: flex;
	flex-direction: column;
	align-items: center;
	background-size: cover;
	justify-content: center;
	margin-bottom: 30px;
}

.content {
  position: fixed;
  bottom: 0;
  background: rgba(0, 0, 0, 0.5);
  color: #f1f1f1;
  width: 100%;
  padding: 30px;
}

.topnav {
  overflow: hidden;
  background-color: #000000;
  height: 25rem;
  align-items: center;
  align-content: center;
  text-align: center;
  margin: 2px;
}

.topnav a {
  float: center;
  display: inline-block ;
  color: #f2f2f2;
  text-align: center;
  padding: 15px 15px 15px 15px;
  text-decoration: none;
  font-size: 17px;
  margin: 3px;
}

.topnav a:hover {
  background-color: #66ff66;
  color: black;
}

#logo-container img {
   width:40%;
   height: auto;
   float: center;
}



.active {
  background-color: #4CAF50;
  color: white;
}

.topnav .icon {
  display: none;
}

@media screen and (max-width: 600px) {
  .topnav a:not(:first-child) {display: none;}
  .topnav a.icon {
    float: center;
    display: block;
  }
}

@media screen and (max-width: 600px) {
  .topnav.responsive {position: relative;}
  .topnav.responsive .icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  .topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
}

#Livello_1_copia{
right: 0; bottom: 10rem; top: 2rem;
min-width: 100%; min-height:100%;
width: auto; height: auto;
z-index: 100;
background: repeat;
background-size: cover;

display: block;
 position: absolute;
 pointer-events: none;
 color: whitesmoke;
}


.svg{
  fill:#ffffff;
  padding-top: 15rem;
  top: 20rem;
  height: 100%;
  z-index: 800;
}

/*OVERLAY_Box-container della galleria*/
.overlays {
  display: flex;
  flex-wrap: wrap;
  content: '';
  position: absolute;
  background: rgba(0, 0, 0, 0);
  border-radius: 5px;
  top: 25rem;
  right: 5rem;
  left: 5rem;
  align-items: center;
  margin:7%;
}

div.child:hover {
  cursor: crosshair;
}


/*Parent*/
.parent {
  display: flex;
  flex-wrap: wrap;
  top: 30rem;
  padding-top: 0rem;
  z-index: 50;


}

/*Child=Figlio del genitore= contenitore sigole foto*/
.child {
  flex: 1 0 20%; /* explanation below */
  margin: 6px;
  height: flex;
  background: rgba(0, 0, 0, 0);
  align-self: center;
  border-radius: 6px;
  margin-bottom: 50px;
}

/*Img del figlio*/
.child img {
   max-width: 100%;
   height: flex;
   margin: 0;
   bottom: 10rem;
   border-radius: 6px;
   margin-bottom: 6px;

}

.overlay p {
  font-size:1vw;
  font-weight: bold;
  color:  #00ff00;
}

.child .overlay {
margin-bottom: -40px;
background: rgb(0, 0, 0);
  background: rgba(0, 0, 0, 0.5); /* Black see-through */
  border-radius: 6px;
  color: #f1f1f1;
  height: 100%;
   width: 100%;
     transition: .30s ease;
  opacity:0;
  color: white;
  font-size: 13px;
  text-align: center;

}

#Avatar:hover .overlay {
  opacity: 1;
}

#Avatar1:hover .overlay {
  opacity: 1;
}
#Avatar2:hover .overlay {
  opacity: 1;
}
#Avatar3:hover .overlay {
  opacity: 1;
}
#Avatar4:hover .overlay {
  opacity: 1;
}
#Avatar5:hover .overlay {
  opacity: 1;
}
#Avatar6:hover .overlay {
  opacity: 1;
}
#Avatar7:hover .overlay {
  opacity: 1;
}
#Avatar8:hover .overlay {
  opacity: 1;
}
#Avatar9:hover .overlay {
  opacity: 1;
}
#Avatar10:hover .overlay {
  opacity: 1;
}
#Avatar11:hover .overlay {
  opacity: 1;
}
#Avatar12:hover .overlay {
  opacity: 1;
}
#Avatar13:hover .overlay {
  opacity: 1;
}
#Avatar14:hover .overlay {
  opacity: 1;
}
#Avatar15:hover .overlay {
  opacity: 1;
}


/*OVERBOX TESTO IMG*/
.overbox {
  background-color: #4CAF50;
  position: absolute;
  top: 2px;
  left: 0;
  right: 0;
  color: #ffffff;
  z-index: 100;
  -webkit-transition: all 300ms ease-out;
  -moz-transition: all 300ms ease-out;
  -o-transition: all 300ms ease-out;
  -ms-transition: all 300ms ease-out;
  transition: all 300ms ease-out;
  opacity: 0;
  max-width: 30vh;
  height: 24vh;
  padding: 130px 20px;
  flex: 1 0 20%; /* explanation below */
  border-radius: 6px;
  margin: 6px;
  font-size: 10px;
}

.child:hover .overbox { opacity:50; }
.child .overtext {
  -webkit-transition: all 300ms ease-out;
  -moz-transition: all 300ms ease-out;
  -o-transition: all 300ms ease-out;
  -ms-transition: all 300ms ease-out;
  transition: all 300ms ease-out;
  transform: translateY(40px);
  -webkit-transform: translateY(40px);
}

.child .title {
  font-size: 2.5em;
  text-transform: uppercase;
  opacity: 50%;
  transition-delay: 0.1s;
  transition-duration: 0.2s;
}
.child:hover .title,
.child:focus .title {
  opacity: 1;
  transform: translateY(0px);
  -webkit-transform: translateY(0px);
}

.child .tagline {
  font-size: 0.8em;
  opacity: 0;
  transition-delay: 0.2s;
  transition-duration: 0.2s;
}
.child:hover .tagline,
.child:focus .tagline {
  opacity: 1;
  transform: translateX(20px);
  -webkit-transform: translateX(0px);
}

/* - fine . OVERBOX TESTO IMG*/


#videogallery{
  top: 10rem;
}

video {
  object-fit: cover;
  width: 100vw;
  height: 100vh;
  position: fixed;
  top: 0;
  left: 0;
  z-index: -100;
}


.footer {
   position: fixed;
   left: 0;
   bottom: 0;
   width: 100%;
   background-color:  #4CAF50;
   color: #ffffff;
   text-align: center;
   margin-top: auto;
}

.bg-modal{
  width: 100%;
	height: 100%;
  background-color: rgba(63,191,63,0.64);
  position: fixed;
  top:0;
  justify-content: center;
  align-items: center;
  display: none;
}

.modal-content {
	height: 500px;
	width: 500px;
	background-color: white;
  border-radius: 4px;
  text-align: center;
  padding: 20px;
  position: relative;

}

#fotopopup{
 width: 100%;
  }

  .close {
	position: absolute;
	top: 0;
	right: 10px;
	font-size: 42px;
	color: #333;
	transform: rotate(45deg);
	cursor: pointer;
	&:hover {
		color: #666;
	}

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>PINSTRIPE GRILLZ</title>
    <script type="text/javascript" src="gallery\js\jquery.js"></script>
    <script type="text/javascript" src="gallery\js\main.js"></script>
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
    <link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.css" rel="stylesheet"/>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<link href="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js">
    <link rel="stylesheet" href="gallery\css/main.css">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

  </head>
  <body class="body">

    <header>
      <div class="topnav" id="myTopnav">
        <div id="logo-container"><a href="index.html"><img src="https://i.ibb.co/FgJ2BYn/PINSTRIPE-Logo-Site.png" alt="PINSTRIPE-Logo-Site" border="0">
        </div>

                  <a href="gallery.html.html">Gallery</a>
                  <a href="contact.html">Contact</a>
                  <a href="about.html">About</a>
                  <a href="javascript:void(0);" class="icon" onclick="myFunction()">

          <i class="fa fa-bars"></i>
        </a>
      </div>



    </header>

    <div class="embed-responsive embed-responsive-16by9">
      <video playsinline autoplay muted loop id="videogallery">
          <source src="gallery\img\bg_2.mp4" type="video/mp4">
      </video>
    </div>


    <div class="overlays">

      <div class="child" id="Avatar15"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>White&yellow gold snakes @maibunia</p></div>
      </div>

      <div class="child" id="Avatar14"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>@dg_bladee 🏝</p></div>
      </div>

      <div class="child" id="Avatar13"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>xxxstxr</p></div>
      </div>

      <div class="child" id="Avatar12"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>@ziskasecuris</p></div>
      </div>

      <div class="child" id="Avatar11"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>LV fangs @lui.vi</p></div>
      </div>

      <div class="child" id="Avatar10"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>@prettypukee coin</p></div>
      </div>

      <div class="child" id="Avatar9"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>Black gold biohazard @freddy.boy_bstrd</p></div>
      </div>

      <div class="child" id="Avatar8"><img src="https://i.ibb.co/7SPJ5Jz/VL.jpg" alt="VL" border="0">
        <div class="overlay"><p>Silver</p></div>
      </div>

      <div class="child" id="Avatar7"><img src="gallery\img/skll.jpg" >
        <div class="overlay"><p>10x10 cobalt chrome</p></div>
      </div>

      <div class="child" id="Avatar6"><img src="gallery\img/4.jpg" >
        <div class="overlay"><p>@dg_bladee</p></div>
      </div>

      <div class="child" id="Avatar5"><img src="gallery\img/ggvlff.jpg" >
        <div class="overlay"><p>@imran_potato</p></div>
      </div>

      <div class="child" id="Avatar4"><img src="gallery\img/spnet.jpg" >
        <div class="overlay"><p>Spiderweb</p></div>
      </div>

      <div class="child" id="Avatar3"><img src="gallery\img/Evil.jpg" >
        <div class="overlay"><p>Evil / @yungsherman95</p></div>
      </div>

      <div class="child" id="Avatar2"><img src="gallery\img/shrk.jpg" >
        <div class="overlay"><p>Razor shark teeth</p></div>
      </div>

      <div class="child" id="Avatar1"><img src="gallery\img/wirte.jpg" >
        <div class="overlay"><p>8 bottom Barbwire</p></div>
      </div>



    </div>

<div class="svg-container unclickable"  onclick="return false">
      <svg class="svg 1.1 svg-container" id="Livello_1_copia" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px"
  	 y="0px" viewBox="0 0 722.3 312.2" style="enable-background:new 0 0 722.3 312.2; transform: scale(1,-1)" xml:space="preserve">
     <g>
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  </svg>

  <svg class="svg 1.1 svg-container" id="Livello_1_copia" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px"
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</svg>

</div>


<div class="footer">
  <p>© PinStripe Custom Jewelery .</p>
</div>

    <script>
    function myFunction() {
      var x = document.getElementById("myTopnav");
      if (x.className === "topnav") {
        x.className += " responsive";
      } else {
        x.className = "topnav";
      }
    }
    </script>

<!-- Modal Section -->

<div class="bg-modal">
 <div class="modal-content">
   <div class="close">+</div>
   <img src="" alt="" id="fotopopup">
 </div>
</div>

  </body>
</html>

Solution

You can retrieve the image from the clicked element and pass it as the src of your element inside the popup like this :

window.onload=function(){

  var selectable = document.getElementsByClassName('child');
  for(var i = 0, j = selectable.length; i < j; i++) {
    selectable[i].addEventListener("click", function(e) {

      document.getElementById('fotopopup').setAttribute('src', e.target.attributes['src'].value);
      document.querySelector('#text-block').innerHTML = e.target.nextElementSibling.innerHTML;
    document.querySelector('.bg-modal').style.display = "flex";
  });
  }


  document.querySelector('.close').addEventListener("click", function() {
    document.querySelector('.bg-modal').style.display = "none";
  });


}

HTML of modal

<div class="bg-modal">
 <div class="modal-content">
   <div class="close">+</div>
   <img src="" alt="" id="fotopopup">

   <span id="text-block"></span>
 </div>
</div>

Live demo