拖拽小案例

拖拽小案例
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div class="drag" style="left:0;top:0;width:100px;height:100px">拖拽小案例</div>
    <style>
      .drag {
    
    
        background-color: skyblue;
        position: absolute;
        line-height: 100px;
        text-align: center;
        padding: 10px;
      }
    </style>
    <script>
      // 获取DOM元素;
      let dragDiv = document.getElementsByClassName('drag')[0];
      // 鼠标按下事件 处理程序
      let putDown = function(event) {
    
    
        dragDiv.style.cursor = 'move';

        // 页面的所有宽度 - 移动盒子的宽度 获取出来可以移动的距离 如果窗口大小不变，这个就是一个常亮
        const CLIENT_WIDTH = window.innerWidth - dragDiv.clientWidth;
        const CLIENT_HEIGHT = window.innerHeight - dragDiv.clientHeight;

        let offsetX = parseInt(dragDiv.style.left); // 获取当前的x轴距离
        let offsetY = parseInt(dragDiv.style.top); // 获取当前的y轴距离

        // let innerX = event.clientX - dragDiv.offsetLeft; // 获取鼠标在方块内的x轴距
        // let innerY = event.clientY - dragDiv.offsetTop; // 获取鼠标在方块内的y轴距

        let innerX = event.clientX - offsetX; // 获取鼠标在方块内的x轴距
        let innerY = event.clientY - offsetY; // 获取鼠标在方块内的y轴距

        // 鼠标移动的时候不停的修改div的left和top值
        document.onmousemove = function(event) {
    
    
          event.preventDefault();

          let pl = event.clientX - innerX;
          let pt = event.clientY - innerY;

          pl = pl <= 0 ? 0 : pl >= CLIENT_WIDTH ? CLIENT_WIDTH : pl;
          pt = pt <= 0 ? 0 : pt >= CLIENT_HEIGHT ? CLIENT_HEIGHT : pt;

          dragDiv.style.left = pl + 'px';
          dragDiv.style.top = pt + 'px';
        };

        // 鼠标抬起时，清除绑定在文档上的mousemove和mouseup事件
        // 否则鼠标抬起后还可以继续拖拽方块
        document.onmouseup = function() {
    
    
          document.onmousemove = null;
          document.onmouseup = null;
        };
      };
      // 绑定鼠标按下事件
      dragDiv.addEventListener('mousedown', putDown, false);
    </script>
  </body>
</html>
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