make a draggable div in another div

I have a draggable div designed by code below. Now I want to put this div in an other div. I want my first div move just inside of second div not allover the web page. I put <div> </div> any where of my code but did not see what I want.

The code is:

//Make the DIV element draggagle:
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;
  z-index: 9;
  
  text-align: center;
  border: 1px solid #d3d3d3;
}

#mydivheader {
  padding: 10px;
  cursor: move;
  z-index: 10; 
}

@media print {
    body{
        width: 21cm;
        height: 29.7cm;
        margin: 0 0mm 0mm 0mm; 
        /* change the margins as you want them to be. */
   } 
}

<div id="mydiv">
  <div id="mydivheader">my text</div>
</div>

Can anyone help me please? ;-)

Solution

We could restrict the movement of draggable element within the dimensions of parent element. Thats what is done in below lines of code:

<!DOCTYPE html>
<html>
<style>
#wrapper {
    width: 200px;
    height: 200px;
    background-color: grey;
    position: relative;
}
#mydiv {
  position: absolute;
  z-index: 9;
  
  text-align: center;
  border: 1px solid #d3d3d3;
}

#mydivheader {
  padding: 10px;
  cursor: move;
  z-index: 10; 
}

@media print {
    body{
        width: 21cm;
        height: 29.7cm;
        margin: 0 0mm 0mm 0mm; 
        /* change the margins as you want them to be. */
   } 
}
</style>
<body>
<div id="wrapper">
<div id="mydiv">
  <div id="mydivheader">my text</div>
</div>
</div>

<script>
//Make the DIV element draggagle:
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))     {
        elmnt.style.top = (parentElement.offsetHeight - elmnt.offsetHeight) + "px"; 
        return;
      }
    if(elmnt.offsetLeft < 0){elmnt.style.left = "0px";return}
    if(elmnt.offsetLeft > (parentElement.offsetWidth - elmnt.offsetWidth)){
        elmnt.style.left = (parentElement.offsetWidth - elmnt.offsetWidth) + "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>

</body>
</html>

The additional js code added is:

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

These are just a couple of checks, to not change element's position if it goes beyond the dimensions of parent element.