使用 mouse事件 实现一个可拖曳的 div

HTML

<div id="xxx"></div>

CSS

*{margin:0; padding: 0;}

div{
  border: 1px solid red;xx
  position: absolute;
  top: 0;
  left: 0;
  width: 100px;
  height: 100px;
}

JavaScript

var dragging = false                                //是否可拖曳，默认不能
var position = null                                 //记录上一次的坐标，默认空

xxx.addEventListener('mousedown',function(e){       //监听鼠标按下事件，获取xy坐标
  dragging = true
  position = [e.clientX, e.clientY]
})

document.addEventListener('mousemove', function(e){ //监听鼠标移动事件
  if(dragging === false){return}
  const x = e.clientX                               //获取鼠标移动的坐标
  const y = e.clientY
  const deltaX = x - position[0]                    //鼠标位移的坐标等于这一次减上一次的坐标
  const deltaY = y - position[1] 
  const left = parseInt(xxx.style.left || 0)        //把位移的像素变成数字，进行运算
  const top = parseInt(xxx.style.top || 0)
  xxx.style.left = left + deltaX + 'px'             //把位移的距离放到div上
  xxx.style.top = top + deltaY + 'px'
  position = [x, y]                                //把这一次的坐标记录到下一次上
})
document.addEventListener('mouseup', function(e){  //监听鼠标松开事件，不在拖曳
  dragging = false
})