<el-select
    v-model="valuesList"
    multiple
    collapse-tags
    filterable
    :filter-method="filterValue"
    @change="selectAll"
    @focus="focus"
    @clear="clearAll"
    placeholder="请选择">
      <el-option
        v-for="item in options"
        :key="item.value"
        :label="item.label"
        :value="item.value"
      >
    </el-option>
  </el-select>
  
  data(){
    return{
      valuesList: [],
      oldValues: [],
      currentVal: '',
      options: [{
        value: '0',
        label: '全选'
      },
        {
        value: '1',
        label: '黄金糕'
      }, {
        value: '2',
        label: '双皮奶'
      }, {
        value: '选项3',
        label: '蚵仔煎'
      }, {
        value: '3',
        label: '龙须面'
      }, {
        value: '4',
        label: '北京烤鸭'
      }],
      optionsCopy: [{
        value: '0',
        label: '全选'
      },
        {
        value: '1',
        label: '黄金糕'
      }, {
        value: '2',
        label: '双皮奶'
      }, {
        value: '选项3',
        label: '蚵仔煎'
      }, {
        value: '3',
        label: '龙须面'
      }, {
        value: '4',
        label: '北京烤鸭'
      }]
    }
  }
  
  methods :{
    selectAll(val) {
      const valArr = []
      this.optionsCopy.forEach(item => {
        valArr.push(item.value)
      })
      // 全选
      if (val.includes('0')) {
        this.valuesList = valArr
        this.oldValues = valArr
      }
      // 点击其他取消全选
      if (val.includes('0') && val.length === this.options.length - 1) {
        if (val[0] === '0') {
          const duplicatedValues = [...new Set(this.valuesList)].filter(item => val.includes(item)).splice(1)
          this.valuesList = duplicatedValues
          this.oldValues = []
        }
      }
      // 反选
      if (val.length === this.oldValues.length - 1 && !val.includes('0')) {
        this.valuesList = []
        this.oldValues = []
      }
      // 当其他全部选择时全选
      if (this.valuesList.length === this.options.length - 1 && this.oldValues.length === 0) {
        this.valuesList.unshift('0')
        this.oldValues = this.valuesList
      }
      // 选择搜索出的结果后
      if (this.options.length < this.optionsCopy.length) {
        if (val[0] === '0') {
          const duplicatedValues = [...new Set(this.valuesList)].filter(item => val.includes(item)).splice(1)
          this.valuesList = duplicatedValues
          this.oldValues = []
        }
        if (this.valuesList.length === this.optionsCopy.length && this.oldValues.length === 0) {
          this.valuesList.unshift('0')
          this.oldValues = this.valuesList
        }
      }
    },
    // 搜索过滤方法
    filterValue(currentVal) {
      if(currentVal.length > 0) {
        this.options = this.optionsCopy.filter(item => {
          if(currentVal === item.label.substring(0, currentVal.length)) {
            return true
          }
        })
        this.currentVal = currentVal
      } else {
        this.options = this.optionsCopy
        this.currentVal = ''
      }
    },
    // 聚焦时
    focus() {
      if (this.currentVal.length > 0) {
        this.options = this.optionsCopy.filter(item => {
          if(this.currentVal === item.label.substring(0, this.currentVal.length)) {
            return true
          }
        })
        return
      } else {
        this.options = this.optionsCopy
      }
      if (this.currentVal) {
        this.options = this.optionsCopy
      }
    },
    clearAll() {
      this.valuesList = []
      this.oldValues = []
    }
  }