Implementation of element shuttle frame performance optimization

v-infinite-scroll="pageDown"
:infinite-scroll-immediate="false"

<el-checkbox-group
        v-show="!hasNoMatch && data.length > 0"
        v-model="checked"
        :size="size"
        :class="{ 'is-filterable': filterable }"
        class="el-transfer-panel__list"
        v-infinite-scroll="pageDown"
        :infinite-scroll-immediate="false"
      >
        <el-checkbox
          class="el-transfer-panel__item"
          :label="item[keyProp]"
          :disabled="item[disabledProp]"
          :key="item[keyProp]"
          v-for="item in filteredData">
            <option-content :option="item"></option-content>
        </el-checkbox>
</el-checkbox-group>

 v-for="item in showData">

data (data) {
    const checked = [];
    this.showData = data.slice(0, this.pageSize);

    const filteredDataKeys = this.filteredData.map(
    (item) => item[this.keyProp]
    );
    this.checked.forEach((item) => {
    if (filteredDataKeys.indexOf(item) > -1) {
        checked.push(item);
    }
    });
    this.checkChangeByUser = false;
    this.checked = checked;
},
filteredData (filteredData) {
    this.showData = filteredData.slice(0, this.pageSize);
 }

pageDown () {
    const l = this.showData.length;
    const totalLength = this.filteredData.length
    l < totalLength && 
    (this.showData = this.filteredData.slice(0, l + this.pageSize > totalLength ?
    totalLength : l + this.pageSize));
},

    pageDown () {
      const totalLength = this.filteredData.length
      if((this.curIndex*this.pageSize) < totalLength){
        this.curIndex++
        const targetLength = this.curIndex * this.pageSize 
        const endPoint = targetLength > totalLength ? totalLength : targetLength
        const startPoint = endPoint - this.pageSize > 0 ? endPoint - this.pageSize : 0
        this.showData = this.filteredData.slice(startPoint, endPoint);
        this.$refs.scrollContainer.$el.scrollTop = "1px" //Scroll the bar to the top and connect to the next page. 0 may trigger boundary problems.}
    }

The InfiniteScroll command only provides downward scrolling. We can extend this command and add upward scrolling listener mounted(){
        this.$refs.scrollContainer.$el.addEventListener('scroll', this.pageUp)
    },
    beforeDestroy(){
        this.$refs.scrollContainer.$el.removeEventListener('scroll', this.pageUp)
    },

    pageUp(e){
      if(e.target.scrollTop === 0 && this.curIndex> 1){
        this.curIndex --
        const endPoint = this.curIndex * this.pageSize 
        const startPoint = (this.curIndex-1)* this.pageSize 
        this.showData = this.filteredData.slice(startPoint, endPoint);
        const el = this.$refs.scrollContainer.$el
        el.scrollTop = el.scrollHeight - el.clientHeight - 1 // Scroll to the bottom and connect to the previous page. -1 prevents border problems.
      }
    },

    initScroll(){
        this.curIndex = 1
        this.$refs.scrollContainer.$el.scrollTop = 0
    },

    data(){
        ...
        this.initScroll()
        ...
    },
    filteredData (filteredData) {
      ...
      this.initScroll()
    }