TypeError: Cannot read property '0' of undefined

1、错误描述

 [Vue warn]: Error in render: "TypeError: Cannot read property '0' of undefined         vue.runtime.esm.js:587
"
found in
---> 
<ElTableFooter>
  <ElTable>
         
   <CurrentStock> at srcviews	ablecontrolCenterCurrentStock.vue
           
    <ElRow>
             
     <ControlCenter> at srcviews	ablecontrolCenterindex.vue
               
      <AppMain> at srcviewslayoutcomponentsAppMain.vue
                 
        <Layout> at srcviewslayoutLayout.vue
                   
           <App> at srcApp.vue
                     
             <Root>

TypeError: Cannot read property '0' of undefined                    vue.runtime.esm.js:1737 
    
at element-ui.common.js:13072
    
at Proxy.renderList (vue.runtime.esm.js:3701)
    
at Proxy.render (element-ui.common.js:13060)
    
at VueComponent.Vue._render (vue.runtime.esm.js:4540)
    
at VueComponent.updateComponent (vue.runtime.esm.js:2784)
    
at Watcher.get (vue.runtime.esm.js:3138)
    
at Watcher.run (vue.runtime.esm.js:3215)
    
at flushSchedulerQueue (vue.runtime.esm.js:2977)
    
at Array.<anonymous> (vue.runtime.esm.js:1833)
    
at flushCallbacks (vue.runtime.esm.js:1754)

TypeError: Cannot read property '0' of undefined

2、错误原因

<template>
    <el-table :data="tabList" style="height:400px;overflow-y:auto;" show-summary sum-text="合计" :summary-method="formatSummary">
        <el-table-column label="名称" prop="name" align="center"></el-table-column>
        <el-table-column v-for="(m,index) in tabHeadList" :key="index" align="center" :label=m :formatter="formatZ" :prop="m"></el-table-column>
        <!-- <el-table-column label="合计">
            <template slot-scope="scope">
                {{scope.row}}
            </template>
        </el-table-column> -->
    </el-table>
</template>

formatSummary(param) {
   console.log(param)
}

       formatSummary函数需要一个返回值，如果没有的话，会出现报错

3、解决办法

formatSummary(param) {
   const { columns, data } = param;
   const sums = [];
   columns.forEach((column, index) => {
   if (index === 0) {
       sums[index] = '合计';
       return;
   }
   const values = data.map(item => Number(item[column.property]));
   if (!values.every(value => isNaN(value))) {
        sums[index] = values.reduce((prev, curr) => {
        const value = Number(curr);
        if (!isNaN(value)) {
            return prev + curr;
        } else {
            return prev;
        }
       }, 0);
        sums[index] = Math.round(sums[index]);
        } 
    });

    return sums;
}