中间件是否可以访问中间件错误处理程序？

Question

I am currently using Express and trying to handle a JsonWebToken error gracefully.

I have two middleware functions I have created, one that extracts a user from a jwt token, and one that handles any route errors for specific usecases.

const userExtractor = async (req, res, next) => {
    const token = req.token
    if (token) {
        const decodedToken = jwt.verify(token, process.env.SECRET)
        const user = await User.findById(decodedToken.id)
        req.user = user
    }

    next()
}

If token is included and verified, and finds a user from my database with the id inside the token, a user object is attached to any incoming requests.

I am trying to error handle when someone sends a faulty token. The error occurs with jsonwebtoken .verify method.

Desktop\backend\node_modules\jsonwebtoken\verify.js:75
    return done(new JsonWebTokenError('invalid token'))

My error handle should be handling this specific error, however I am not sure if how middlewares work this is possible.

const errorHandler = (error, req, res, next) => {
    if (error.name === "JsonWebTokenError") {
        return res.status(400).json({error: 'invalid token has been sent'})
    }
    next(error)
}

And yes, I have initiated both middlewares, with the error handler specifically being the last middleware used at the end.

// Util middleware
app.use(middleware.tokenExtractor)
app.use(middleware.userExtractor)

// Routes
app.use('/auth', authRouter);
app.use('/api/me', meRouter)

app.get("/", (req, res) => {
    res.send("Hello World!");
});

app.use(middleware.errorHandler)

Answer 1

To handle an error in a middleware need to try catch section so with return the next(error) , middleware error will get the error that happened in the middleware

try like the below code

const userExtractor = async (req, res, next) => {
    try {
        const token = req.token
        if (token) {
            const decodedToken = jwt.verify(token, process.env.SECRET)
            const user = await User.findById(decodedToken.id)
            req.user = user
        }

        next()
    } catch (error) {
        return next(error);
    }
}