function next(err) { // signal to exit route if (err && err === 'route') { return done(); } // signal to exit router if (err && err === 'router') { return done(err) } // max sync stack if (++sync > 100) { return setImmediate(next, err) } var layer = stack[idx++] // end of layers if (!layer) { return done(err) } if (layer.method && layer.method !== method) { next(err) } else if (err) { layer.handle_error(err, req, res, next); } else { layer.handle_request(req, res, next); } sync = 0 }