Server Side development with Node.js and Koa.js Quick Start Guide

Error event listener

Error event listeners can be defined with app.on('error'). They are particularly useful for centralized logging and error reporting. The error listeners receive all errors that are thrown in the middleware chain, except the ones that are caught and are neither rethrown or emitted using app.emit(). To define an error handler, refer to this code:

app.on('error', err => {  // log errors  console.error("server error", err);});

If no event listener is defined, then app.onerror is used. This simply outputs the error to stdout unless app.silent is true, err.status is 404, or err.expose is set to true.

If an error is thrown in the middleware chain and it is not possible to respond to the client, the context object is also passed ...