div拖拽改变大小的demo

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .box {
      border: 1px solid #d6d6d6;
      position: absolute;
    }

    .left-border {
      width: 4px;
      height: 200px;
      background-color: #00c0ff;
      position: absolute;
      cursor: w-resize;
    }

    .top-border {
      width: 200px;
      height: 4px;
      background-color: #00c0ff;
      position: absolute;
      cursor: n-resize;
    }

    .right-border {
      width: 4px;
      height: 200px;
      background-color: #00c0ff;
      position: absolute;
      cursor: e-resize;
    }

    .bottom-border {
      width: 200px;
      height: 4px;
      background-color: #00c0ff;
      position: absolute;
      cursor: s-resize;
    }
  </style>
</head>
<body>

<div class="box" style="width:200px;height:200px;top:200px;left:600px;">
  <div class="left-border" id="left" style="left:0;top:0;"></div>
  <div class="top-border" id="top" style="left:0;top:0;"></div>
  <div class="right-border" id="right" style="right:0;top:0;"></div>
  <div class="bottom-border" id="bottom" style="left:0;bottom:0;"></div>
</div>

</body>

<script>

  let u_left = document.getElementById('left')
  let u_top = document.getElementById('top')
  let u_right = document.getElementById('right')
  let u_bottom = document.getElementById('bottom')

  let currentX = 0, // 用来记录鼠标按下时的横坐标
    currentY = 0, // 用来记录鼠标按下时的纵坐标
    currentDivWidth = 0, // 鼠标按下时div的宽度
    currentDivHeight = 0, // 鼠标按下时div的高度
    currentDivX = 0,  // 鼠标按下时div的横坐标
    currentDivY = 0 // 鼠标按下时div的纵坐标
  let currentCanvasDiv = null // 鼠标按下时存放要改变大小的div
  let currentBorder = null // 鼠标按下时存放当前拖动的边

  // 绑定鼠标按下事件
  u_left.onmousedown = mouseDown
  u_top.onmousedown = mouseDown
  u_right.onmousedown = mouseDown
  u_bottom.onmousedown = mouseDown

  function mouseDown(event) {
    currentX = event.clientX
    currentY = event.clientY
    const path = event.path || (event.composedPath && event.composedPath()) // 获取当前点击事件冒泡所经过的路径同时解决火狐的兼容问题
    currentCanvasDiv = path[1]
    currentBorder = path[0].id
    currentDivWidth = parseInt(currentCanvasDiv.style.width)
    currentDivHeight = parseInt(currentCanvasDiv.style.height)
    currentDivX = parseInt(currentCanvasDiv.style.left)
    currentDivY = parseInt(currentCanvasDiv.style.top)
    document.addEventListener("mousemove", eval(currentBorder + 'Move'))
    document.addEventListener("mouseup", mouseUp)
  }

  function mouseUp() {
    document.removeEventListener("mousemove", eval(currentBorder + 'Move'))
    document.removeEventListener("mouseup", mouseUp)
  }

  // 拖动左侧边
  function leftMove(event) {
    let _X = event.clientX
    let _width = currentDivWidth + currentX - _X // 拖动后div的宽度
    if (_width <= 200) { // 设置可以拖动的最小宽度
      u_bottom.style.width = u_top.style.width = currentCanvasDiv.style.width = 200 + 'px'
      currentCanvasDiv.style.left = currentDivWidth + currentDivX - 200 + 'px' // 使左侧边向左移动，否则改变宽度时div会默认向右增宽
    } else {
      u_bottom.style.width = u_top.style.width = currentCanvasDiv.style.width = _width + 'px'
      currentCanvasDiv.style.left = currentDivX + _X - currentX + 'px'
    }
  }

  function rightMove(event) {
    let _X = event.clientX
    let _width = currentDivWidth + _X - currentX
    if (_width <= 200) {
      u_bottom.style.width = u_top.style.width = currentCanvasDiv.style.width = 200 + 'px'
    } else {
      u_bottom.style.width = u_top.style.width = currentCanvasDiv.style.width = _width + 'px'
    }
  }

  function bottomMove(event) {
    let _Y = event.clientY
    let _height = currentDivHeight + _Y - currentY
    if (_height <= 200) {
      u_left.style.height = u_right.style.height = currentCanvasDiv.style.height = 200 + 'px'
    } else {
      u_left.style.height = u_right.style.height = currentCanvasDiv.style.height = _height + 'px'
    }
  }

  function topMove(event) {
    let _Y = event.clientY
    let _height = currentDivHeight + currentY - _Y
    if (_height <= 200) {
      u_left.style.height = u_right.style.height = currentCanvasDiv.style.height = 200 + 'px'
      currentCanvasDiv.style.top = currentDivHeight + currentDivY - 200 + 'px'
    } else {
      u_left.style.height = u_right.style.height = currentCanvasDiv.style.height = _height + 'px'
      currentCanvasDiv.style.top = currentDivY + _Y - currentY + 'px'
    }
  }

</script>

</html>
div拖拽改变大小的demo

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