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expressloggingerror-handlingjoi

How to log Celebrate validation errors to the console in Express.js?

I have an Express.js app in which I'm trying to log the validation errors returned by Celebrate to the console so that I can analyze them with the logging service that I use (which is GCP's Cloud Logging).

I'm currently just using the error handling middleware provided by Celebrate as suggested in the documentation:

// app.js

const { errors } = require('celebrate');

...

app.use(errors());

...

How can I extend the middleware (without re-implementing it) so that it also logs the validation errors to the console?

Solution

  • The simplest way to achieve this seems to be by defining another error middleware before the Celebrate error middleware, that checks whether the error is a Celebrate error (using the isCelebrateError method) and if so it logs it to the console:

    // app.js

const { errors, isCelebrateError } = require('celebrate');

...


// middleware to log Celebrate validation errors
app.use((err, req, res, next) => {
    if (isCelebrateError(err)) {
        console.error(err);
    }
    next(err);
});

// Celebrate middleware to return validation errors
app.use(errors());

...

    It is important to include the logging middleware before Celebrate's errors() middleware since errors() returns a JSON response and no other middleware is run after it (you can check out the Celebrate source code for the implementation details of errors()).