Dragable div does not work in touch screen

I have a dragable div that works in computer very well but today I checked in touch screen and knew that it does not move !!! In my java script code I have onmousemove , is there any alternative for that in touchscreen? Can any body tell me what to do to solve this ? BTW I want this work in both touch screen and computer, not just in touch screen
My dragable div code is blow.

<div id="wrapper" style="border: 0.1vw solid gray;">
    <div id="mydiv">
        <img src="image/cs.png">
    </div>
</div>

<script>
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;
            
            let parentElement = elmnt.parentElement;
            if(elmnt.offsetTop < 0){elmnt.style.top = "0px"; return;}
            if(elmnt.offsetTop > (parentElement.offsetHeight - elmnt.offsetHeight)-2)     {
                elmnt.style.top = (parentElement.offsetHeight - elmnt.offsetHeight-2) + "px"; 
                return;
              }
            if(elmnt.offsetLeft < 0){elmnt.style.left = "0px";return}
            if(elmnt.offsetLeft > (parentElement.offsetWidth - elmnt.offsetWidth)-2){
                elmnt.style.left = (parentElement.offsetWidth - elmnt.offsetWidth-2) + "px";
                return;
            }
            
            // 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;
          }
        }
</script>