Node.js with express throw Error versus the following (error)

Question

Can someone please provide information about the time when it comes up in the node.js Express application to cause this error:

throw new Error('my error'); 

or pass this error using a callback, usually labeled as follows:

 next(error); 

and could you please explain what each of them will do in the context of the Express application?

for example, here is an express function associated with URL parameters:

 app.param('lineup_id', function (req, res, next, lineup_id) { // typically we might sanity check that user_id is of the right format if (lineup_id == null) { console.log('null lineup_id'); req.lineup = null; return next(new Error("lineup_id is null")); } var user_id = app.getMainUser()._id; var Lineup = app.mongooseModels.LineupModel.getNewLineup(app.system_db(), user_id); Lineup.findById(lineup_id, function (err, lineup) { if (err) { return next(err); } if (!lineup) { console.log('no lineup matched'); return next(new Error("no lineup matched")); } req.lineup = lineup; return next(); }); }); 

The line commented "// should I create my own error here?" I could use "throw new Error (" xyz ")", but what exactly is it to do? Why is it usually better to pass the error to the "next" callback?

Another question: how do I get "throw new Error (" xyz ") to display in the console as well as in the browser when I'm in development?

Answer 1

In general terms, the error path should be followed, not its throw, for any errors in the program you can pass the error object to the “next” one, you also need to define an error handler so that all errors passed to the next one can be processed correctly

http://expressjs.com/guide/error-handling.html