Node.js Web Apps With Express Error handling
Example
Basic docs can be found here
app.get('/path/:id(\\d+)', function (req, res, next) { // please note: "next" is passed
if (req.params.id == 0) // validate param
return next(new Error('Id is 0')); // go to first Error handler, see below
// Catch error on sync operation
var data;
try {
data = JSON.parse('/file.json');
} catch (err) {
return next(err);
}
// If some critical error then stop application
if (!data)
throw new Error('Smth wrong');
// If you need send extra info to Error handler
// then send custom error (see Appendix B)
if (smth)
next(new MyError('smth wrong', arg1, arg2))
// Finish request by res.render or res.end
res.status(200).end('OK');
});
// Be sure: order of app.use have matter
// Error handler
app.use(function(err, req, res, next)) {
if (smth-check, e.g. req.url != 'POST')
return next(err); // go-to Error handler 2.
console.log(req.url, err.message);
if (req.xhr) // if req via ajax then send json else render error-page
res.json(err);
else
res.render('error.html', {error: err.message});
});
// Error handler 2
app.use(function(err, req, res, next)) {
// do smth here e.g. check that error is MyError
if (err instanceof MyError) {
console.log(err.message, err.arg1, err.arg2);
}
...
res.end();
});
Appendix A
// "In Express, 404 responses are not the result of an error,
// so the error-handler middleware will not capture them."
// You can change it.
app.use(function(req, res, next) {
next(new Error(404));
});
Appendix B
// How to define custom error
var util = require('util');
...
function MyError(message, arg1, arg2) {
this.message = message;
this.arg1 = arg1;
this.arg2 = arg2;
Error.captureStackTrace(this, MyError);
}
util.inherits(MyError, Error);
MyError.prototype.name = 'MyError';
