feature: add drag select component (#1249)

src/components/DragSelect/index.vue

@@ -0,0 +1,61 @@
+<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>