因此，我尝试使用axios从API提取数据，当我在前端代码上“ npm start”时，它返回未处理拒绝（TypeError）：无法读取未定义的属性“ data”。我试图找出问题所在，但我不知道。

这是我的后端代码：

// //config
require('dotenv').config()
const express = require('express')
const app = express()
const mongoose = require('mongoose')

var cors = require('cors');
app.use(cors());
mongoose.connect(process.env.DATABASE_URL,{
    useCreateIndex: true,useNewUrlParser: true,useUnifiedTopology: true
  }
)

app.use((req,res,next) => {
  res.header('access-control-allow-origin','*')
  next();
})


const db = mongoose.connection
db.on('error',(error) => console.error(error))
db.once('open',()=> console.log('connected'))

const gasRouter = require('./routes/gas-routes')
app.use('/api/gas',gasRouter)

const stockRouter = require('./routes/stock-routes')
app.use('/api/stock',stockRouter)
//
// const wisataPrimer = require("./routes/route.js")
// app.use('/')
app.listen(5001,() => console.log('server started'))

这是我的前端（操作）代码：

import {GET_GASTYPE,GET_STOCKTABLE} from './actionTypes';
import axios from 'axios'

export const getGasType = () => dispatch => {
    axios.get('/api/gas')
    .then(res =>
        dispatch({
        type: GET_GASTYPE,payload: res.data
    }))
    .catch(err => 
    dispatch((err.response.data,err.response.status))
);
};

export const getGasStatus = () => dispatch => {
    axios.get('/api/stock')
        .then(res =>
            dispatch({
            type: GET_STOCKTABLE,payload: res.data
        }))
    .catch(err => 
        dispatch((err.response.data,err.response.status))
    );
};

你们能告诉我代码中哪一部分错误吗？谢谢。