Check out example codes for "html dragging get mouse position". It will help you in understanding the concepts better.

Code Example 1

<!DOCTYPE html>
<html>

<head>
  <meta name="viewport" 
        content="width=device-width, 
        initial-scale=1.0, 
        user-scalable=no" />
  <title>Drag/Drop/Bounce</title>
  <style>
    #container {
      width: 100%;
      height: 400px;
      background-color: #333;
      display: flex;
      align-items: center;
      justify-content: center;
      overflow: hidden;
      border-radius: 7px;
      touch-action: none;
    }
    #item {
      width: 100px;
      height: 100px;
      background-color: rgb(245, 230, 99);
      border: 10px solid rgba(136, 136, 136, .5);
      border-radius: 50%;
      touch-action: none;
      user-select: none;
    }
    #item:active {
      background-color: rgba(168, 218, 220, 1.00);
    }
    #item:hover {
      cursor: pointer;
      border-width: 20px;
    }
  </style>
</head>

<body>

  <div id="outerContainer">
    <div id="container">
      <div id="item">

      </div>
    </div>
  </div>

  <script>
    var dragItem = document.querySelector("#item");
    var container = document.querySelector("#container");

    var active = false;
    var currentX;
    var currentY;
    var initialX;
    var initialY;
    var xOffset = 0;
    var yOffset = 0;

    container.addEventListener("touchstart", dragStart, false);
    container.addEventListener("touchend", dragEnd, false);
    container.addEventListener("touchmove", drag, false);

    container.addEventListener("mousedown", dragStart, false);
    container.addEventListener("mouseup", dragEnd, false);
    container.addEventListener("mousemove", drag, false);

    function dragStart(e) {
      if (e.type === "touchstart") {
        initialX = e.touches[0].clientX - xOffset;
        initialY = e.touches[0].clientY - yOffset;
      } else {
        initialX = e.clientX - xOffset;
        initialY = e.clientY - yOffset;
      }

      if (e.target === dragItem) {
        active = true;
      }
    }

    function dragEnd(e) {
      initialX = currentX;
      initialY = currentY;

      active = false;
    }

    function drag(e) {
      if (active) {
      
        e.preventDefault();
      
        if (e.type === "touchmove") {
          currentX = e.touches[0].clientX - initialX;
          currentY = e.touches[0].clientY - initialY;
        } else {
          currentX = e.clientX - initialX;
          currentY = e.clientY - initialY;
        }

        xOffset = currentX;
        yOffset = currentY;

        setTranslate(currentX, currentY, dragItem);
      }
    }

    function setTranslate(xPos, yPos, el) {
      el.style.transform = "translate3d(" + xPos + "px, " + yPos + "px, 0)";
    }
  </script>
</body>

</html>

Code Example 2

//  JavaScript

document.addEventListener("dragover", function(e){
    e = e || window.event;
    var dragX = e.pageX, dragY = e.pageY;

    console.log("X: "+dragX+" Y: "+dragY);
}, false);

//  jQuery

$("body").bind("dragover", function(e){
    var dragX = e.pageX, dragY = e.pageY;

    console.log("X: "+dragX+" Y: "+dragY);
});

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