React component throws a const undefined error after refreshing-CodePudding

I'm trying to come up with a basic dashboard that would display the results of SQL counts inside card elements using React and upon much frustration, I was able to render the component using this code.

import axios from "axios";
import React, { useEffect, useState } from "react";
import { Card, Col, Row } from 'antd';
import "../App.css";

function Dashboard() {
    const [cuentaClientes, setcuentaClientes] = useState([]);
    const [cuentaVehiculos, setcuentaVehiculos] = useState([]);
  
    useEffect(() => {
      axios.get("http://localhost:3002/api/clientes/contar").then((data) => {
        setcuentaClientes(data.data);
        });

      axios.get("http://localhost:3002/api/vehiculos/contar").then((data) => {
        setcuentaVehiculos(data.data);
        });
    }, []);
    
    const yyy = cuentaVehiculos.map((vehiculo) => {
        return {
            key: vehiculo.total,
            total: vehiculo.total,
        };
    });
  
    const xxx = cuentaClientes.map((cliente) => {
        return {
            key: cliente.cantidad,
            cantidad: cliente.cantidad,
        };
    });

    return (
        <div>
            <Row gutter={[16, 16]}>
                <Col span={8}>
                    <Card title="Clientes" bordered={false}>
                        <p>{xxx[0].cantidad}</p>
                    </Card>
                </Col>
                <Col span={8}>
                    <Card title="Vehiculos" bordered={false}>
                        <p>{yyy[0].total}</p>
                    </Card>
                </Col>
            </Row>
        </div>
    );
}

export default Dashboard;

However, whenever I refresh the page for whatever reason, the browser throws an error saying variables xxx and yyy are undefined. The error only goes away when I remove their references, like this:

from <p>{xxx[0].cantidad}</p> to <p></p>

Then, in order to see the count again, I just add the references again.

How can I prevent this from happening?

Thank you all in advance.

CodePudding user response：

return (
        <div>
            <Row gutter={[16, 16]}>
                <Col span={8}>
                    <Card title="Clientes" bordered={false}>
                        <p>{xxx?.[0]?.cantidad ?? ''}</p>
                    </Card>
                </Col>
                <Col span={8}>
                    <Card title="Vehiculos" bordered={false}>
                        <p>{yyy?.[0]?.total ?? ''}</p>
                    </Card>
                </Col>
            </Row>
        </div>
    );

xxx?.[0]?.cantidad ?? '' Initially it will return an empty string or you can write xxx?.[0]?.cantidad ?? 'Loading...'. Once it is loaded it will show the required data.