you shouldn't really ever throw, Connect / Express will catch what they can
but not in async callbacks etc. The error handling middleware work just
like regular middleware, so they're executed in sequence, however *usually*
you'll have only one, typically defined as the very last middleware,
something like:
app.use(function(err, req, res, next){
// handle however you like, special-case based on
// error properties, messages, request conditions etc
// here we'll just render an error page
res.status(err.status || 500);
res.render('error', { error: err });
})
errorHandler() is just the "fancy" looking one for development (if you want
it) that outputs HTML exceptions.
also for future reference there's an express google
group: https://groups.google.com/forum/?fromgroups#!forum/express-js
On Wednesday, 14 March 2012 09:47:15 UTC-7, HG wrote:
>
> Hi!
>
> I've read the http://expressjs.com/guide.html#error-handling and gone
> through this:
> http://stackoverflow.com/questions/7151487/error-handling-principles-for-nodejs-express-apps
> I've also written couple of pages of tests and I still cannot figure
> out how I should return errors to the users (REST json API). So, can
> somebody explain it to me.
>
> I'm trying to handle errors from middleware and from routes. I want to
> send different responseCodes (like invalid query, data not found,
> internal server error) as responses to the API.
>
> First, it took me a while to figure out that
> "app.use(express.errorHandler({ showStack: true, dumpExceptions: true
> })); " needs to have the "app.use(app.router); " called before it.
> Yes, I can now read it from the page, but it was not that clear to me.
> So, I have probably missed something else too.
>
> So, some questions now:
> - The doc says that there is a "app.error(function(err, req, res,
> next){" that get's called with "next(err);" However, the stackoverflow
> thread says that it's deprecated and now its "app.use(function(err,
> req, res, next) {". Which one is correct?
> - The doc says that app.error is called with next(err) - but what is
> in err? There is complicated example, 'function NotFound(msg){', ok,
> it's not that complicated, but I didn't think I need to do that much
> code for the error. The code at
>
> https://github.com/visionmedia/express/blob/master/examples/error-pages/app.js
> uses more simple new Error('message'). What should the err contain?
> - According to doc, app.error is called with next(err) or by throw
> err. The writer in stackoverflow says throwing is bad practice - why?
> What is the difference (except that code doesn't continue after
> throw)?
> - Am I right in assuming that I cannot have express.errorHandler and
> app.error at the same time. express.errorHandler sounds like a good
> way to do errors (if it can for instance server json also), however it
> seems to me that it always returns 500 (var err = new
> Error('Failure');err.status = 401;next(err); -> still shows 500 as
> statusCode.
>
> So, I guess I should use "app.use(function(err, req, res, next) {" to
> get some other errors than 500. But I'm not really sure if I should
> "throw { status: 401, message: "failure" }" or call "next(err)" with
> "err = new Error('failure'); err.status=401".
>
> How do you guys handle these?
>
> --
> HG.
>
>
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