element-UI checkbox 多选框

http://element-cn.eleme.io/#/zh-CN/component/checkbox
这里的例子中，数据源是普通数组.

这里为了需求，将普通数组改为对象数组.

<template>
  <el-checkbox :indeterminate="isIndeterminate" v-model="checkAll" @change="handleCheckAllChange">全选</el-checkbox>
  <div style="margin: 15px 0;"></div>
  <el-checkbox-group v-model="checkedCities" @change="handleCheckedCitiesChange">
    <el-checkbox v-for="city in cities" :label="city.id" :key="city.id">{{city.label}}</el-checkbox>
  </el-checkbox-group>
</template>
<script>
  const cityOptions = [{id:1,label:'上海'},{id:2,label:'北京'},{id:3,label:'广州'}, {id:4,label: '深圳'}];
  export default {
    data() {
      return {
        checkAll: false,
        checkedCities: [1,2],
        cities: cityOptions,
        isIndeterminate: true
      };
    },
    methods: {
      handleCheckAllChange(val) {
        this.checkAll =  !!this.checkAll;
        let checked = cityOptions.map(function(item){return item.id;});
        this.checkedCities = this.checkAll ? checked : [];
        this.isIndeterminate = false;
      },
      handleCheckedCitiesChange(value) {
        let checkedCount = value.length;
        this.checkAll = checkedCount === this.cities.length;
        this.isIndeterminate = checkedCount > 0 && checkedCount < this.cities.length;
      }
    }
  };
</script>