Node / Express good error handling approach?

Question

I have several mongoose route api functions and I would like to know what is the best approach in error handling. Below is an example function. In the first part, I am doing some mongoose database querying, then I execute async function with exec, then I catch any errors, else I am processing data further.

exports.getStornoData = function(req,res,next) {        
    Produkt.aggregate([         
        {
            "$unwind":"$DemonstratorWerte"
        },      
        {
            $match: {
                "DemonstratorWerte.Demonstrator":+req.params.demo_id, "DemonstratorWerte.RstorniertDemo.B":true
            }       
        },...
    ]).exec(function(err, result) {
            if (err) {
                next(err);              
                res.status('404').send();
                }

            else {                  
                    //process data...
                    res.locals.stornierungen = stornierungenArray;                  
                    next();             
                }
        })
    }

Is that error handling approach acceptable? How can I catch most errors and output (or collect) them on a place where it does not disturb user experience?

if (err) {
    next(err);              
    res.status('404').send();
}

and is this correct with next(err) and sending the status of 404 with method chaining thereafter?

Answer 1

See the express error handling documentation .

Instead of returning a 404 in your own middleware functions, you should define your own "custom" error handling middleware:

function errorHandler (err, req, res, next) {
   // Decide what to return to client here based on type of error.  
}

Make sure to define error-handling middleware last, after other app.use() and routes calls.