nodejs重定向而没有任何错误

Question

在编辑产品时，如果输入无效，我将connect-flash与express-session一起使用以显示错误。问题是有时错误不会显示，我必须刷新页面才能看到它。

这是我在app.js上的代码

const session = require('express-session');
const MongoDBStore = require('connect-mongodb-session')(session);
const flash = require('connect-flash');
const store = new MongoDBStore({
    uri: <my mongodb connection>, 
    collection: 'sessions',
});

app.use(session({
    secret: 'my secret', 
    resave: false, 
    saveUninitialized: false,
    store: store
}));

app.use(flash());

controller.js上的代码

const productValidator = (req, res, title, imageUrl, price, description) => {
    let hasError = false;
    const invalidTitle = validator.isEmpty(title);
    const validImageUrl = validator.isURL(imageUrl);
    const validPrice = validator.isNumeric(price);
    const validDescription = validator.isLength(description, {min: 5});

    if (invalidTitle) {
        req.flash('error', {message: 'Title is required', input: 'title'});
        hasError = true;
    }

    if (!validImageUrl) {
        req.flash('error', {message: 'Image should be valid url', input: 'imageUrl'});
        hasError = true;
    }

    if (!validPrice) {
        req.flash('error', {message: 'Price should be number', input: 'price'});
        hasError = true;
    }

    if (!validDescription) {
        req.flash('error', {message: 'Description should be more than or equal 5 character', input: 'description'});
        hasError = true;
    }

    return hasError;
}

module.exports.postEditProduct = async (req, res) => {
    const backURL = req.header('Referer');
    const prodId = req.body.productId;
    const updatedTitle = req.body.title;
    const updatedPrice = req.body.price;
    const updatedImageUrl = req.body.imageUrl;
    const updatedDesc = req.body.description;

    try {
        const product = await Product.findById(prodId);

        if (product.userId.toString() !== req.user._id.toString()) {
            return res.redirect('/');
        }

        const isNotValid = productValidator(req, res, updatedTitle, updatedImageUrl, updatedPrice, updatedDesc);

        if (isNotValid) {
            return res.redirect(backURL);
        }

        product.title = updatedTitle;
        product.price = updatedPrice;
        product.imageUrl = updatedImageUrl;
        product.description = updatedDesc;
        await product.save();

        // console.log(product);

        res.redirect('/admin/products');
    } catch (e) {
        res.status(400).send(e);
    }
};

请帮助我对nodejs有点陌生。谢谢。