Puppeteer异步函数返回值赋值失败，打印结果为undefined

你遇到的核心问题是async函数的返回值是Promise对象，不是你直接return的包含breakfast、lunch的菜单对象。所以const menu = getMenu()得到的是一个Promise实例，而非预期的菜单数据，自然menu.breakfast会显示undefined。

有两种简单的方式可以获取到正确的菜单对象：

方法一：用async/await包裹调用逻辑 #

await只能在async函数内部使用，所以可以把调用代码放到一个async函数里：

const puppeteer = require("puppeteer");

async function getMenu() {
    console.log("Opening the browser...");
    const browser = await puppeteer.launch({
        headless: true
    });
    const page = await browser.newPage();
    await page.goto('https://pra.ufpr.br/ru/ru-centro-politecnico/', {waitUntil: 'domcontentloaded'});
    console.log("Content loaded...");

    const fullMenu = await page.evaluate(() => {
        return {
            day: document.querySelector('#conteudo div:nth-child(3) p strong').innerText,
            breakfastFood: document.querySelector('tbody tr:nth-child(2)').innerText,
            lunchFood: document.querySelector('tbody tr:nth-child(4)').innerText,
            dinnerFood: document.querySelector('tbody tr:nth-child(6)').innerText
        };
    });

    await browser.close();
    
    return {
        breakfast: fullMenu.day + "\nCafé da Manhã:\n" + fullMenu.breakfastFood,
        lunch:     fullMenu.day + "\nAlmoço:\n" + fullMenu.lunchFood,
        dinner:    fullMenu.day + "\nJantar:\n" + fullMenu.dinnerFood
    };
};

// 用async函数包裹调用
async function main() {
    const menu = await getMenu();
    console.log(menu.breakfast);
}

main();

方法二：用Promise的.then()处理返回值 #

如果不想额外写async函数，直接用Promise的then方法读取结果：

const puppeteer = require("puppeteer");

async function getMenu() {
    // 原函数内容保持不变
};

getMenu().then(menu => {
    console.log(menu.breakfast);
});

可以给爬虫加个错误处理，避免页面元素找不到时程序崩溃，比如在page.evaluate里做元素判空，或者给整个getMenu函数加try/catch：

async function getMenu() {
    try {
        console.log("Opening the browser...");
        const browser = await puppeteer.launch({
            headless: true
        });
        const page = await browser.newPage();
        await page.goto('https://pra.ufpr.br/ru/ru-centro-politecnico/', {waitUntil: 'domcontentloaded'});
        console.log("Content loaded...");

        const fullMenu = await page.evaluate(() => {
            const dayEl = document.querySelector('#conteudo div:nth-child(3) p strong');
            const breakfastEl = document.querySelector('tbody tr:nth-child(2)');
            const lunchEl = document.querySelector('tbody tr:nth-child(4)');
            const dinnerEl = document.querySelector('tbody tr:nth-child(6)');
            
            return {
                day: dayEl ? dayEl.innerText : '未获取到日期',
                breakfastFood: breakfastEl ? breakfastEl.innerText : '未获取到早餐',
                lunchFood: lunchEl ? lunchEl.innerText : '未获取到午餐',
                dinnerFood: dinnerEl ? dinnerEl.innerText : '未获取到晚餐'
            };
        });

        await browser.close();
        
        return {
            breakfast: fullMenu.day + "\nCafé da Manhã:\n" + fullMenu.breakfastFood,
            lunch:     fullMenu.day + "\nAlmoço:\n" + fullMenu.lunchFood,
            dinner:    fullMenu.day + "\nJantar:\n" + fullMenu.dinnerFood
        };
    } catch (error) {
        console.error('获取菜单出错:', error);
        return {
            breakfast: '获取失败',
            lunch: '获取失败',
            dinner: '获取失败'
        };
    }
};

内容的提问来源于stack exchange，提问作者João