实现提示框可拖拽（针对antd vue中的a-modal提示框）

1. 在 utils 中新建 directives.js 文件

import Vue from 'vue'

// v-drag-modal: 弹窗拖拽
Vue.directive('drag-modal', (el, bindings, vnode) => {
  Vue.nextTick(() => {
    let { visible, destroyOnClose } = vnode.componentInstance
    // 防止未定义 destroyOnClose 关闭弹窗时dom未被销毁，指令被重复调用
    if (!visible) return
    let modal = el.getElementsByClassName('ant-modal')[0]
    let header = el.getElementsByClassName('ant-modal-header')[0]
    let left = 0
    let top = 0
    // 未定义 destroyOnClose 时，dom未被销毁，关闭弹窗再次打开，弹窗会停留在上一次拖动的位置
    if (!destroyOnClose) {
      left = modal.left || 0
      top = modal.top || 0
    }
    // top 初始值为 offsetTop
    top = top || modal.offsetTop
    // 点击title部分拖动
    header.onmousedown = e => {
      let startX = e.clientX
      let startY = e.clientY
      header.left = header.offsetLeft
      header.top = header.offsetTop
      el.onmousemove = event => {
        let endX = event.clientX
        let endY = event.clientY
        modal.left = header.left + (endX - startX) + left
        modal.top = header.top + (endY - startY) + top
        modal.style.left = modal.left + 'px'
        modal.style.top = modal.top + 'px'
      }
      el.onmouseup = event => {
        left = modal.left
        top = modal.top
        el.onmousemove = null
        el.onmouseup = null
        header.releaseCapture && header.releaseCapture()
      }
      header.setCapture && header.setCapture()
    }
    // 点击表单部分拖动
    // modal.onmousedown = e => {
    //   let startX = e.clientX
    //   let startY = e.clientY
    //   header.left = header.offsetLeft
    //   header.top = header.offsetTop
    //   el.onmousemove = event => {
    //     let endX = event.clientX
    //     let endY = event.clientY
    //     modal.left = header.left + (endX - startX) + left
    //     modal.top = header.top + (endY - startY) + top
    //     modal.style.left = modal.left + 'px'
    //     modal.style.top = modal.top + 'px'
    //   }
    //   el.onmouseup = event => {
    //     left = modal.left
    //     top = modal.top
    //     el.onmousemove = null
    //     el.onmouseup = null
    //     header.releaseCapture && header.releaseCapture()
    //   }
    //   header.setCapture && header.setCapture()
    // }
  })
})

2. 在main.js中引入

import '@/utils/directives.js'

3. 在使用a-modal的地方添加v-drag-modal

    <a-modal
      class="po-search"
      width="700px"
      :dialog-style="{ top: '200px' }"
      :visible="isAddSku"
      :destroyOnClose="true"
      @cancel="isAddSku = false"
      v-drag-modal
    >