how to use errorhandler middleware in express 4.x - node.js

Question

I tried to use middleware errorhandler， but doesn't work, even i set process.env.NODE_ENV ='development'
below is the server code:
var express = require('express');
var app = express();
var errorhandler = require('errorhandler');
var notifier = require('node-notifier');
process.env.NODE_ENV = 'development'; //just purposely do this, see if it can work
if (process.env.NODE_ENV == 'developmet') {
app.use(errorhandler({ log: errorNotification }));
}
function errorNotification(err, str, req) {
var title = 'Error in' + req.method + '' + req.url;
notifier.notify({
title: title,
message: str
});
}
app.get('/', function (req, res, next) {
nonexist(); //the error is still captured Native node.js not errorhandler
res.send('this is home page!');
next();
});
app.listen(1338);
no matter what kind of options i tried in errorhandler, it still doesn't work.
can anyone help me to check any setting is wrong?

Answer 1

Error handling is declared after all your other routes. Express moves through routes from top to bottom or left to right (if you imagine all your code on one line).
You can capitalize on this by putting a splat route after all your other routes, and it will be activated if no other exact route matches. This is how you can do an error 404 page.
It's why you build your routes like this (which will prepare you for React Router 'switch component', if you move into React coding):
GET /test/:slug
GET /test
GET /
Here is an example of a splat route and following that, your error handler middleware:
// Try switching the order of these first two
app.get('/', async (req, res, next) => {
return res.status(200).send('test')
})
app.get('*', async (req, res, next) => {
return res.status(404).send('error 404') // res.render('error/404')
})
// ERRORS
app.use(async (err, req, res, next) => {
// if next() is called with a parameter, which can be anything,
// this middleware will fire
res.status(500).send('error 500') // res.render('error/500')
throw err
})
// Try replacing your default route with this now
app.get('/', async (req, res, next) => {
return next('Extreme detonations')
})
You do not need the async functions as I have shown here, but I do it as a matter of convention so I can always slap await in there. I use explicit returns to prevent any issues with sending headers after they are already sent, and because async functions return promises, so explicit return will resolve them.
All my routes generally look like this:
app.get('/admin', async (req, res, next) => {
try {
if (!req.user) throw 'garbageUser'
const poop = await something()
return res.render('template', {
data: obj,
bonusData
})
} catch (e) {
if (e === 'garbageUser') {
log.add(`illegal: ${req.originalUrl} from ${sniffer.getClientIp(req)}`)
return res.render('403')
}
return next(e)
}
})
This should hopefully be informative for you and offer some code to forensically analyze. The Express error handler middleware takes a 4th parameter in the first position called err which contains the value passed into next().
Check out the Express documentation again after studying this, and it will make much more sense :)
To answer your question:
var express = require('express');
var app = express();
// You can add these back now that you understand
// var errorhandler = require('errorhandler');
// var notifier = require('node-notifier');
function handleErrors(error) {
console.log('I'm telling your mom about this: ' + error);
}
app.get('/', function(req, res, next) {
return next('REALLY BAD');
return res.send('this is home page!');
});
// Remember, this must be after all your other routes
app.use(function(err, req, res, next) {
console.log('Problem occurred, we could put logic here...');
console.log('Error was: ' + err);
if (err === 'REALLY BAD') {
handleErrors(err);
}
next();
});
app.listen(1338);
Try commenting this out now return next('REALLY BAD'); and run it again. You should see "this is home page!".
When you call next() with no parameter in it, Express treats it as no error. If you pass any value in, like next(err) or next('Chicken tastes good'), you will see err defined with that value in your error handling middleware.