How to manage HTTP errors in Node.js

Question

Hi I'm developing my first Node.js application and I found my first issue in something really basic, I can't catch the HTTP errors (404, 500, ...)

I've followed the doc (I think so) but I suppose that I'm missing something.

This is my code:

var express = require('express')
app = express()
app.use(express.logger('dev'));

app.get('/', function(req, res) {
    res.send('Hellow World!!!')
})
app.use(app.router);
app.use(function(err, req, res, next) {
    console.error('Oh!! ERROR');
    console.error('My ERROR: ' + JSON.stringify(err));
});

app.listen(3000);
console.log('Server running at http://127.0.0.1:3000/');

Thanks in advance.

Peter Lyons · Accepted Answer · 2013-01-19 02:49:47Z

2

So the way express works is if it hits the end of the entire stack of middleware and route handlers and nothing has responded yet, it's going to send the fallback 404 response automatically without raising an error. This is why your error handling middleware isn't being called. By default, express doesn't consider a 404 an error, which is probably the right way to think of it.

If you want to customize this, you can put a middleware at the end of your stack to either serve a custom 404 page directly or call next with an error if you prefer that way.

app.get('/'...
app.get('/two'...
app.get(/'three'...

app.use(middleware1...
app.use(middleware2...
app.use(app.router);
app.use(function (req, res, next) {
    //Option 1: respond here
    return res.status(404).render('my_404_view');
    //Option 2: trigger error handler
    return next(new Error('404ed!'));
}

Option 2 will trigger your error handling middleware. There you will have to get info from the error object to determine the desired view to render and status code to send. I personally define an errors.NotFound class that has a 404 code and lets me render a friendly 404 page view.

edited Jan 19, 2013 at 2:49

answered Jan 18, 2013 at 21:32

Peter Lyons

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4 Comments

Roberto Over a year ago

Hi @peter-lyons, thanks for your quick answer, now my error middleware is triggered, but I have a problem, It's triggered always, even if a route is found (and the page correctly returned). I though that if one of the routes responses the rest of middlewares are not triggered... Am I wrong ?

Peter Lyons Over a year ago

Are you calling next() after rendering a page? Once the page is rendered, you should not call next(). Only call next() from a middleware that is in the "middle" of the processing stack.

Roberto Over a year ago

It's very odd only is triggered the first time, the second call works fine, the route is this: app.get('/', function(req, res) { res.send('Index Page!!!') // Middleware page is only triggered the first time })

Roberto Over a year ago

Forgot my last comment, It's working perfectly, but I was testing from a browser and the 404 error was triggered for the request /favicon.ico That it was made automatically by the browser, sorry for silly question :-)

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