How do I prevent node from logging an exception to the console in my NextJS/Express app? - node.js

Question

I have an Express application that runs a blog in a NextJS app, very similar to the example in their repo
I have set it up so that my app runs a query to fetch a blog article, and if the result is empty it throws a NotFoundException.
I catch this exception in my NextJS _error.js file, which is similar to a React error boundary, where I route the user to my 404 page. This part works fine.
The problem I'm having is that this exception is logged to the node console even though I'm not logging it when catching the exception. This pollutes our company's logging software with all our 404's
Is there some node/express setting I'm missing here that prevents the logging of exceptions? Here's my Express process error handler:
process.on('unhandledRejection', (reason, promise) =>
console.error(`Unhandled Rejection at: ${promise}.\nreason: ${reason.stack || reason}`));
I know there is a log there, but the format of the one I want to eliminate is different to this, so I'm confident this is not the source.

Answer 1

I won't pretend to know what's going on, but my best guess is that next.js is logging the error somewhere. I did some digging and it appears there's an error logger in the server code that will log on errors unless a quiet property is set on the server:
https://github.com/zeit/next.js/blob/canary/packages/next-server/server/next-server.ts#L105:
return this.run(req, res, parsedUrl)
.catch((err) => {
this.logError(err)
res.statusCode = 500
res.end('Internal Server Error')
})
Here's the sig and body for the logError function:
private logError(...args: any): void {
if (this.quiet) return
// tslint:disable-next-line
console.error(...args)
}
If you look at the documentation for using the next API with a custom server, it notes the following options object properties that can be passed to the constructor:
The next API is as follows:
next(opts: object)
Supported options:
dev (bool) whether to launch Next.js in dev mode - default false
dir (string) where the Next project is located - default '.'
quiet (bool) Hide error messages containing server information - default false
conf (object) the same object you would use in next.config.js - default {}
When constructing the next object, try passing quiet as true to see if it resolves your issue:
const express = require('express')
const next = require('next')
const port = parseInt(process.env.PORT, 10) || 3000
const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev, quiet: true })
const handle = app.getRequestHandler()
The docs also mentions errors are logged in non-production environments (identified when process.env.NODE_ENV !== 'production'), so I would also check to ensure you're setting NODE_ENV to 'production' when starting your application:
NODE_ENV=production node server.js
I hope this helps!

Answer 2

In express you can setup an ErrorMiddleware.
After all your routes declaration, put
server.use(function(req, res, next) {
handler(req, res).catch(e => {
// use rejected promise to forward error to next express middleware
next(e)
})
});
Like this, when you reject a Promise, next(e) will send your error to next middleware. I usually setup a middleware where i send error, and then i manage all errors in one single function (based on statusCode error,...).