express js 4 how to serve json results without rendering any views /css
If you're making any calls to res.render such as in an error handler that are generated by the 'express generate', then you'll see the error you described. For a json API service you probably don't need to render anything so just don't call render(), instead call res.send() with the status res.status set to 404 or 500.
So basically, replace this:
app.use(function(err, req, res, next) { res.render('error', { message: err.message, error: err });});with this:
app.use(function(err, req, res, next){ res.status(err.status || 500); res.send({ message: err.message, error: err }); return;});