<template>
  <div v-drag class='div-class'></div>   
  // 定位最好用absoulte或者fixed,relative极大几率不生效
</template>

<script>
   export default {
     name: 'modalBlock',
     props: {},
     data () {
       return {}
     },
     directives: {
       drag (el) {
         el.style.cursor = 'move'
         
         el.onmousedown = function (e) {
           var disx = e.pageX- el.offsetLeft;
           var disy = e.pageY- el.offsetTop;
           
           if (e.preventDefault) {
              e.preventDefault()
           } else {
              e.returnValue = false  // 解决快速频繁拖动滞后问题
           }
           
           document.onmousemove = function (e) { 
           // 鼠标位置-鼠标相对元素位置=元素位置
             let left = e.clientX - disx;
             let top = e.clientY - disy;
             // 限制拖拽范围不超出可视区
             if ( left <= 0) {
               left = 5    // 设置成5,离边缘不要太近
             } else if (left > document.documentElement.clientWidth - el.clientWidth) { // document.documentElement.clientWidth屏幕可视区宽度
                left = document.documentElement.clientWidth - el.clientWidth - 5
             }

            if ( top <= 0) {
               top = 5
             } else if (top > document.documentElement.clientHeight - el.clientHeight) {
                top = document.documentElement.clientHeight - el.clientHeight - 5
             }
             el.style.left = left + 'px'
             el.style.top= top + 'px'
           }
           
           document.onmouseup = function () {
             document.onmousemove = document.onmouseup = null
           }
         }
       }
     }
   }
</script>