How to make draggable elements replicate after drag?

I'm making a website on which people would be able to drag and drop shapes to make their own compositions. I want to have 4 shapes that you can drag, but the shape replicates and stays so you can use it as many times as you want.

I know HTML, CSS and a bit of JS and I managed to make the shapes draggable (with some tutorials), but I can't work out how to make them replicate. Any suggestions would be very appreciated! Thanks!

// Make the DIV element draggable:
dragElement(document.getElementById("mydiv"));

function dragElement(elmnt) {
  var pos1 = 0,
    pos2 = 0,
    pos3 = 0,
    pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
    // if present, the header is where you move the DIV from:
    document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;
  } else {
    // otherwise, move the DIV from anywhere inside the DIV:
    elmnt.onmousedown = dragMouseDown;
  }

  function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();
    // get the mouse cursor position at startup:
    pos3 = e.clientX;
    pos4 = e.clientY;
    document.onmouseup = closeDragElement;
    // call a function whenever the cursor moves:
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e = e || window.event;
    e.preventDefault();
    // calculate the new cursor position:
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    pos3 = e.clientX;
    pos4 = e.clientY;
    // set the element's new position:
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
  }

  function closeDragElement() {
    // stop moving when mouse button is released:
    document.onmouseup = null;
    document.onmousemove = null;
  }
}

#mydiv {
  position: absolute;
  top: 100px;
  left: 100px;
  z-index: 9;
  background-color: #ffffffff;
  text-align: center;
  cursor: move;
  transform: translate(-50%, -50%) scale(0.5);
}

<div id="mydiv">
  <div id="mydivheader"><img src="m1.png"></div>
</div>
<script src="drag.js"></script>

Solution

These modifications of the OP's code will do the following when the dragged div is dropped:

make a clone of the dragged div and add it to the <body>
move the dragged div back to its starting position

const mydiv = document.getElementById("mydiv");

// Make the DIV element draggable:
dragElement(mydiv);

function dragElement(elmnt) {
  var pos1 = 0,
    pos2 = 0,
    pos3 = 0,
    pos4 = 0;
  if (document.getElementById(elmnt.id + "header")) {
    // if present, the header is where you move the DIV from:
    document.getElementById(elmnt.id + "header").onmousedown = dragMouseDown;
  } else {
    // otherwise, move the DIV from anywhere inside the DIV:
    elmnt.onmousedown = dragMouseDown;
  }

  function dragMouseDown(e) {
    e = e || window.event;
    e.preventDefault();
    // get the mouse cursor position at startup:
    pos3 = e.clientX;
    pos4 = e.clientY;
    document.onmouseup = closeDragElement;
    // call a function whenever the cursor moves:
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e = e || window.event;
    e.preventDefault();
    // calculate the new cursor position:
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    pos3 = e.clientX;
    pos4 = e.clientY;
    // set the element's new position:
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
  }

  function closeDragElement() {
    // stop moving when mouse button is released:
    document.onmouseup = null;
    document.onmousemove = null;
    
    // ****** start added code ******

    // create a clone of mydiv and append it to body
    const newDiv = mydiv.cloneNode(true);
    document.body.appendChild(newDiv);
    
    // move mydiv back to its starting position
    mydiv.style.top = null;
    mydiv.style.left = null;

    // ****** end added code ******
  }
}

#mydiv {
  position: absolute;
  top: 100px;
  left: 100px;
  z-index: 9;
  background-color: #ffffffff;
  text-align: center;
  cursor: move;
  transform: translate(-50%, -50%) scale(0.5);
}

<div id="mydiv">
  <div id="mydivheader"><img src="https://via.placeholder.com/80/"></div>
</div>
<script src="drag.js"></script>