vue element el-transfer增加拖拽功能

芯资管项目要求el-transfer增加拖拽排序，左右上下互相拖拽功能；
原来的组件不支持拖拽，这里要用个第三方脱宅组件sortablejs

首先安装

 sudo npm i sortablejs --save-dev

html代码

  <template>
  <el-transfer ref=\"transfer\" id=\"transfer\" v-model=\"value\" :data=\"data\">
   <span slot-scope=\"{ option }\" :draggable=\"!option.disabled\" @dragstart=\"drag($event,option)\">{{ option.key }} - {{ option.label }}</span>
  </el-transfer>
</template>```

create

  <script>

   import Sortable from \'sortablejs\'

   export default {
      data() {
        const generateData = _ => {
          const data = []; for (let i = 1; i <= 15; i++) {
            data.push({
              key: i,
              label: `备选项 ${i}`,
              disabled: i % 4 === 0 });
          } return data;
        }; return {
          data: generateData(),
          value: [1, 4],
          draggingKey : null }
      },
      mounted() {
        const transfer = this.$refs.transfer.$el
        const leftPanel = transfer.getElementsByClassName(\"el-transfer-panel\")[0].getElementsByClassName(\"el-transfer-panel__body\")[0];
        const rightPanel = transfer.getElementsByClassName(\"el-transfer-panel\")[1].getElementsByClassName(\"el-transfer-panel__body\")[0];
        const rightEl = rightPanel.getElementsByClassName(\"el-transfer-panel__list\")[0]
        Sortable.create(rightEl,{
          onEnd: (evt) => {
            const {oldIndex,newIndex} = evt;
            const temp = this.value[oldIndex] 
            if (!temp || temp === \'undefined\') {
              return
            }// 解决右边最后一项从右边拖左边，有undefined的问题
            this.$set(this.value,oldIndex,this.value[newIndex])  
            this.$set(this.value,newIndex,temp)
          }
        })
        const leftEl = leftPanel.getElementsByClassName(\"el-transfer-panel__list\")[0]
        Sortable.create(leftEl,{
          onEnd: (evt) => {
            const {oldIndex,newIndex} = evt;
            const temp = this.data[oldIndex] 
            if (!temp || temp === \'undefined\') {
              return
            } // 解决右边最后一项从右边拖左边，有undefined的问题
            this.$set(this.data,oldIndex,this.data[newIndex]) 
            this.$set(this.data,newIndex,temp)
          }
        })
        leftPanel.ondragover = (ev) => {
          ev.preventDefault()
        }
        leftPanel.ondrop = (ev) => {
          ev.preventDefault();
          const index = this.value.indexOf(this.draggingKey) if(index !== -1){ this.value.splice(index,1)
          }
        }
        rightPanel.ondragover = (ev) => {
          ev.preventDefault()
        }
        rightPanel.ondrop = (ev) => {
          ev.preventDefault();  if(this.value.indexOf(this.draggingKey) === -1){ this.value.push(this.draggingKey)
          }
        }
      },
      methods: {
        drag(ev,option) { this.draggingKey = option.key
        }
      }

    } 
</script>