先看一下结果图：

官方文档：https://element.eleme.cn/#/zh-CN/component/checkbox

其中需要注意的几点：

1. 单独选择的时候全选按钮应该变成indeterminate 状态；
2. 在已有部分选择时点击全选秩序添加未选择的元素，而非所有；
3. 页码切换后应当保留当页选择状态；

<template>
  <div class="group">
    <div class="box check">
      <div class="search">
        <el-checkbox class="selectAll" :indeterminate="isIndeterminate" v-model="checkAll" @change="handleCheckAllChange">全选</el-checkbox>
        <el-checkbox @change="handleCheckBackChange">反选</el-checkbox>
      </div>
      <el-form ref="form" label-width="0px" v-loading="loading">
        <el-form-item label="">
          <el-checkbox-group v-model="checkValue" @change="checkChange">
            <el-checkbox v-for="(item, index) in list" :key="index" :label="item.id">{{ item.id }}</el-checkbox>
          </el-checkbox-group>
        </el-form-item>
      </el-form>
      <!-- 分页 -->
      <div class="page">
        <el-pagination :current-page="page" :page-sizes="[15, 20, 30, 40]" :page-size="num" layout="total, sizes, prev, pager, next, jumper" :total="total" @current-change="pageChange" @size-change="sizeChange"></el-pagination>
      </div>
      {{ checkValue }}
    </div>
  </div>
</template>

<script>
import { list } from '@/api/index' // 引入后端接口
export default {
  data() {
    return {
      list: [],
      page: 1,
      num: 30,
      total: 0,
      loading: false,
      checkValue: [], // 已经选择的元素
      isIndeterminate: false, // 全选按钮indeterminate状态
      checkAll: false // 全选按钮是否全选
    }
  },
  mounted() {
    this.getList()
  },
  methods: {
    getList: function(search) { // 获取列表数据
      if (search) {
        this.page = 1
      }
      this.loading = true
      let params = {
        page: this.page,
        num: this.num
      }
      list(params).then(res => { // 请求后端接口获取列表数据
        this.list = res.data.list
        this.total = res.data.total // 总数
        this.loading = false
        this.checkIsIndeterminate() // 每次请求后获取当前页全选按钮的状态，主要用于页码变化
      }).catch(res => {
        this.loading = false
      })
    },
    checkIsIndeterminate: function() { // 判断当前页全选按钮的状态
      let has = 0 // 记录当前页面已选项的条数
      this.list.map(item => {
        if (this.checkValue.indexOf(item.id) != -1) {
          has++
        }
      })
      if (has > 0) { // 有已选项
        if (has == this.list.length) { // 判断是否已经全选
          this.isIndeterminate = false
          this.checkAll = true
        } else {
          this.isIndeterminate = true
          this.checkAll = false
        }
      } else { // 无已选项
        this.isIndeterminate = false
        this.checkAll = false
      }
    },
    checkChange: function(value) { // 多选框的值变化
      this.checkIsIndeterminate()
    },
    handleCheckAllChange(val) { // 全选或全不选
      if (val) { // 全选
        this.list.map(item => {
          if (this.checkValue.indexOf(item.id) == -1) {
            this.checkValue.push(item.id)
          }
        })
      } else { // 全不选
        this.list.map(item => {
          if (this.checkValue.indexOf(item.id) != -1) {
            this.checkValue.splice(this.checkValue.indexOf(item.id), 1)
          }
        })
      }
      this.isIndeterminate = false
    },
    handleCheckBackChange() { // 反选
      let _this = this
      this.list.forEach(item => {
        if (_this.checkValue.indexOf(item.id) != -1) { // 去掉已选项
          _this.checkValue.splice(_this.checkValue.indexOf(item.id), 1)
        } else { // 添加未选项
          _this.checkValue.push(item.id)
        }
      })
      console.log(this.checkValue)
      this.checkIsIndeterminate()
    },
    pageChange: function(page) { // 页码发生变化
      this.page = page
      this.getList()
    },
    sizeChange: function(num) { // 每页条数发生变化
      this.page = 1
      this.num = num
      this.getList()
    }
  }
}
</script>

<style lang="scss" scoped>
.group{
  margin-right: 30px;
  .search{
    margin-bottom: 20px;
  }
  .el-checkbox-group{
    font-size: 17px;
    border-left: 1px solid #DEE2E6;
    .el-checkbox {
      border-right: 1px solid #DEE2E6;
      border-bottom: 1px solid #DEE2E6;
      margin-right: 0;
      width: 20%;
      padding-left: 20px;
      line-height: 44px;
      color: #666666;
    }
    .el-checkbox:nth-child(1), .el-checkbox:nth-child(2), .el-checkbox:nth-child(3), .el-checkbox:nth-child(4), .el-checkbox:nth-child(5){
      border-top: 1px solid #DEE2E6;
    }
  }
}
</style>