Node.js with Express - throw Error vs next(error)

Question

Can someone expound on the times when it's appropriate in a node.js Express app to throw an error like so:

throw new Error('my error'); 

or to pass this error on via the callback usually labelled 'next' like so:

next(error); 

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

for example, here is an express function dealing 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();         });     }); 

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

Another question is - how do I get "throw new Error('xyz')" to show up in the console as well as the browser when I am in development?

Answer 1

In general express follows the way of passing errors rather than throwing it, for any errors in the program you can pass the error object to 'next' , also an error handler need to be defined so that all the errors passed to next can be handled properly

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