front-end/src/components/DragSelect/index.vue

<template>
  <el-select v-model="selectVal" v-bind="$attrs" class="drag-select" multiple>
    <slot/>
  </el-select>
</template>

<script>
import Sortable from 'sortablejs'

export default {
  name: 'DragSelect',
  props: {
    value: {
      type: Array,
      required: true
    }
  },
  computed: {
    selectVal: {
      get() {
        return [...this.value]
      },
      set(val) {
        this.$emit('input', [...val])
      }
    }
  },
  mounted() {
    this.setSort()
  },
  methods: {
    setSort() {
      const el = document.querySelectorAll('.el-select__tags > span')[0]
      this.sortable = Sortable.create(el, {
        ghostClass: 'sortable-ghost', // Class name for the drop placeholder,
        setData: function(dataTransfer) {
          dataTransfer.setData('Text', '')
          // to avoid Firefox bug
          // Detail see : https://github.com/RubaXa/Sortable/issues/1012
        },
        onEnd: evt => {
          const targetRow = this.value.splice(evt.oldIndex, 1)[0]
          this.value.splice(evt.newIndex, 0, targetRow)
        }
      })
    }
  }
}
</script>

<style scoped>
.drag-select >>> .sortable-ghost{
  opacity: .8;
  color: #fff!important;
  background: #42b983!important;
}

.drag-select >>> .el-tag{
  cursor: pointer;
}
</style>