JavaScript实现矩形块大小任意缩放

最近写了一个原生JavaScript实现矩形块大小任意缩放的案例，感觉里面的东西比较的绕,，里分享源码给大家，一起学习一下。

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>原生JavaScript实现矩形块大小任意缩放</title>
</head>
<style>
  * {
    margin: 0;
    padding: 0;
  }

  .box {
    position: relative;
    top: 200px;
    left: 500px;
    width: 500px;
    height: 300px;
    background-color: blueviolet;
  }

  .box>div:nth-child(-n+4) {
    position: absolute;
    width: 5px;
    height: 5px;
    background-color: #cc00ff;
  }

  .box>div:nth-child(n+5) {
    position: absolute;
    background-color: #f30497;
  }

  .box>.dot1 {
    cursor: nw-resize;
    top: -5px;
    left: -5px;
  }

  .box>.dot2 {
    cursor: ne-resize;
    top: -5px;
    right: -5px;
  }

  .box>.dot3 {
    cursor: se-resize;
    bottom: -5px;
    right: -5px;
  }

  .box>.dot4 {
    cursor: sw-resize;
    bottom: -5px;
    left: -5px;
  }

  .box>.line1,
  .box>.line3 {
    width: 500px;
    height: 5px;
  }

  .box>.line1 {
    top: -5px;
    cursor: n-resize;
  }

  .box>.line3 {
    bottom: -5px;
    cursor: s-resize;
  }

  .box>.line2,
  .box>.line4 {
    width: 5px;
    height: 300px;
  }

  .box>.line2 {
    right: -5px;
    cursor: e-resize;
  }

  .box>.line4 {
    left: -5px;
    cursor: e-resize;
  }
</style>

<body>
  <div class="box">
    <div class="dot1"></div>
    <div class="dot2"></div>
    <div class="dot3"></div>
    <div class="dot4"></div>
    <div class="line1"></div>
    <div class="line2"></div>
    <div class="line3"></div>
    <div class="line4"></div>
  </div>
  <script>
    //获取相关元素节点
    let box = document.querySelector(".box");
    let dots = document.querySelectorAll(".box>div:nth-child(-n+4)");
    let lines = document.querySelectorAll(".box>div:nth-child(n+5)");
    // 类边框宽度
    let bd = 5;
    //for循环指定事件对象
    function changeBox([box, dots, lines, bd]) {
      for (let i = 0; i < 4; i++) {
        let { 0: dot1, 1: dot2, 2: dot3, 3: dot4 } = dots;    //dots对象解构
        let { 0: line1, 1: line2, 2: line3, 3: line4 } = lines;    //lines对象解构
        //矩形顶点点击拖动调整大小
        dots[i].onmousedown = function (ev) {
          //点击事件初始化相关值
          let oldY = ev.clientY;   //顶点原本的y值
          let oldX = ev.clientX;   //顶点原本的x值
          let h = box.clientHeight;  //box的高度
          let w = box.clientWidth;  //box的宽度
          let t = box.offsetTop;   //box距离顶部的top值
          let l = box.offsetLeft;   //box距离左边的left值
          window.onmousemove = function (e) {
            let offsetY = e.clientY - oldY;     //鼠标移动y轴偏移量
            let offsetX = e.clientX - oldX;     //鼠标移动x轴偏移量
            //if条件是判断鼠标点击的节点目标对象
            if (i == 0) {
              box.style.height = `${h - offsetY + bd}px`;   //box高度变化
              box.style.top = `${t + offsetY - bd}px`;    //box的top值变化(定位)
              box.style.width = `${w - offsetX + bd}px`;   //box的宽度变化
              box.style.left = `${l + offsetX - bd}px`;    //box的left值变化(定位)
            } else if (i == 1) {
              box.style.height = `${h - offsetY + bd}px`;
              box.style.top = `${t + offsetY - bd}px`;
              box.style.width = `${w + offsetX + bd}px`;
            } else if (i == 2) {
              box.style.height = `${h + offsetY + bd}px`;
              box.style.width = `${w + offsetX + bd}px`;
            } else if (i == 3) {
              box.style.height = `${h + offsetY + bd}px`;
              box.style.width = `${w - offsetX + bd}px`;
              box.style.left = `${l + offsetX - bd}px`;
            }
            //边框线的高度/宽度随着box的大小变化而变化
            line1.style.width = box.style.width;
            line2.style.height = box.style.height;
            line3.style.width = box.style.width;
            line4.style.height = box.style.height;
          }
        }
        //边框点击拖动调整大小
        lines[i].onmousedown = function (ev) {
          //点击事件初始化相关值
          let oldY = ev.clientY;     //顶点原本的y值
          let oldX = ev.clientX;     //顶点原本的x值
          let h = box.clientHeight;    //box的高度
          let w = box.clientWidth;    //box的宽度
          let t = box.offsetTop;     //box距离顶部的top值
          let l = box.offsetLeft;     //box距离左边的left值
          window.onmousemove = function (e) {
            let offsetX = e.clientX - oldX;   //鼠标移动x轴偏移量
            let offsetY = e.clientY - oldY;   //鼠标移动y轴偏移量
            //if条件是判断鼠标点击的节点目标对象
            if (i == 0) {
              box.style.height = `${h - offsetY + bd}px`;
              box.style.top = `${t + offsetY - bd}px`;
            } else if (i == 1) {
              box.style.width = `${w + offsetX + bd}px`;
            } else if (i == 2) {
              box.style.height = `${h + offsetY + bd}px`;
            } else {
              box.style.width = `${w - offsetX + bd}px`;
              box.style.left = `${l + offsetX - bd}px`;
            }
            //边框线的高度/宽度随着box的大小变化而变化
            line1.style.width = box.style.width;
            line2.style.height = box.style.height;
            line3.style.width = box.style.width;
            line4.style.height = box.style.height;
          }
        }
        //鼠标抬起后清除鼠标移动事件
        window.onmouseup = function () {
          window.onmousemove = false;
        }
      }
    }
    changeBox([box, dots, lines, bd])
  </script>
</body>

</html>

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