vue js, vue element, how to add select all

<template>
 <div>
   <el-select v-model="chooseData" multiple placeholder="select" style="width: 300px" @change='selectAll'>
     <el-option v-for="item in selectOptions"
                :key="item.value"
                :label="item.label"
                :value="item.value">
     </el-option>
   </el-select>
 </div>
</template>
<script>
export default {
  data () {
    return {
      selectOptions: [
        { value: 'ALL_SELECT', label: 'select all' },
        { value: '1', label: 'apple' },
        { value: '2', label: 'banana' },
        { value: '3', label: 'orange' },
        { value: '4', label: 'mango' },
        { value: '5', label: 'grape' },
      ],
      oldChooseData: [],
      chooseData: []
    };
  },
  methods: {
    selectAll (val) {
     // Get all possible values
      const allValues = this.selectOptions.map(item => {
        return item.value;
      });
      // Get previously selected values
      const oldVal = this.oldChooseData.length > 0 ? this.oldChooseData : [];

      // if  ALL_SELECT is selected this tim
      if (val.includes('ALL_SELECT')) {
        this.chooseData = allValues;
      }

      //  if  ALL_SELECT selected last time, but not this time => set selected data to []
      if (oldVal.includes('ALL_SELECT') && !val.includes('ALL_SELECT')) {
        this.chooseData = [];
      }


    // If  ALL_SELECT selected last time, and  this time as well, and there is a change in value this time meaning, some previously selected no ALL_SELECT value has been de selected,
then remove ALL_SELECT from list
      if (oldVal.includes('ALL_SELECT') && val.includes('ALL_SELECT')) {
        const index = val.indexOf('ALL_SELECT');
        val.splice(index, 1);
        this.chooseData = val;
      }

      // if ALL_SELECT not selected last time and this time as well,
      // if every other values are selected, add ALL_SELECT to selected data
      if (!oldVal.includes('ALL_SELECT') && !val.includes('ALL_SELECT')) {
        if (val.length === allValues.length - 1) {
          this.chooseData = ['ALL_SELECT'].concat(val);
        }
      }

      //  Save currently selected data for comparison next time
      this.oldChooseData = this.chooseData;
    }
  }
};
</script>
————————————————
：https://blog.csdn.net/sleepwalker_1992/article/details/88876114