Vue makes div height draggable

<template>
  <div id="eagleMapContainer" style="border: 1px solid red;overflow-y: auto;" title="">
    <div id="tz" @mousedown="dragEagle" style="border: 1px solid blue;">
      <div title="Drag to resize" id="move_tz" style="border: 1px solid green;"></div>
    </div>
  </div>
</template>

<script>
  export default {
    name: "eagleMap",
    data() {
      return {}
    },
    methods: {
      dragEagle: function (e) {
        var targetDiv = document.getElementById('eagleMapContainer'); 
        //Get the width and height of the map container when clicked:
        var targetDivHeight = targetDiv.offsetHeight;
        var startX = e.clientX;
        var startY = e.clientY;
        var _this = this;
        document.onmousemove = function (e) {
          e.preventDefault();
          //Get the width and height of the mouse drag: take the absolute value var distX = Math.abs(e.clientX - startX);
          var distY = Math.abs(e.clientY - startY);
          //Drag upwards:
          if (e.clientY < startY) {
            targetDiv.style.height = targetDivHeight + distY + 'px';
          }
          //Drag downwards:
          if (e.clientX < startX && e.clientY > startY) {
            targetDiv.style.height = (targetDivHeight - distY) + 'px';
          }
          if (parseInt(targetDiv.style.height) >= 300) {
            targetDiv.style.height = 300 + 'px';
          }
          if (parseInt(targetDiv.style.height) <= 150) {
            targetDiv.style.height = 150 + 'px';
          }
        }
        document.onmouseup = function () {
          document.onmousemove = null;
        }
      }
    },
  };
</script>

<style scoped>
  #eagleMapContainer {
    position: absolute;
    left: 13%;
    bottom: 10px;
    z-index: 200;
    overflow: hidden;
    visibility: visible;
    width: 200px;
    height: 200px;
  }

  #tz {
    position: absolute;
    right: 1px;
    top: 1px;
    width: 27px;
    height: 20px;
    cursor:ne-resize;
    z-index: 200001;
    background-image: url("");

  }

  #tz:hover {
    background-color: #666;
  }

  #move_tz {
    position: absolute;
    right: 0px;
    top: 0px;
    width: 27px;
    height: 20px;
    cursor:ne-resize;
    z-index: 100;
    background-image: url("");
    background-position: 0px 0px;
  }
</style> 

<!-- Drag and drop small box -->
    <div id="tz" @mousedown="dragEagle">
      <div title="Drag to resize" id="move_tz"></div>
    </div>

// dragEagle(e) {
        var targetDiv = document.getElementById('fuDiv');
        //Get the width and height of the map container when clicked:
        var targetDivHeight = targetDiv.offsetHeight;
        var startX = e.clientX;
        var startY = e.clientY;
        var _this = this;
        document.onmousemove = function (e) {
          e.preventDefault();
          //Get the width and height of the mouse drag: take the absolute value var distY = Math.abs(e.clientY - startY);

          //Drag upwards:
          if (e.clientY < startY) {
            targetDiv.style.height = targetDivHeight - distY + 'px';
          }
          //Drag downwards:
          if (e.clientX < startX && e.clientY > startY) {
            targetDiv.style.height = (targetDivHeight + distY) + 'px';
          }
          if (parseInt(targetDiv.style.height) >= 320) {
            targetDiv.style.height = 320 + 'px';
          }
          if (parseInt(targetDiv.style.height) <= 160) {
            targetDiv.style.height = 160 + 'px';
          }
        }
        document.onmouseup = function () {
          document.onmousemove = null;
        }
      },

  #tz {
    width: 100%;
    height: 5px;
    cursor: s-resize;
    z-index: 200001;
  }
  
  #move_tz {
    width: 100%;
    height: 5px;
    cursor: s-resize;
    z-index: 100;
    background-image: url("");
    background-position: 0px 0px;
  }