app error handling improvements

[jonathanong]

right now, app.onerror is added to the the error event listener automatically. what happens if users don't want to use it? doing app.removeListener('event', app.onerror)` is a little annoying. instead i suggest the following:

• remove app.onerror
• remove app.outputErrors
• at the app.callback() stage, warn/throw if no event listeners have been added
• automatically add the default listener in development

app.callback = function(){
  // ...

  if (!app.listeners('error')) {
    if (this.env === 'development') {
      console.warn('You should add your own error handler.');
      app.on('error', function(err) {
        console.error(err.stack);
      })
    } else if (this.env !== 'test') {
      throw new Error('Add your own error handler!');
    }
  }

  return function(req, res){
  // ..
})

[tj]

how about we remove app.outputErrors (and just imply that stuff in the default handler), and make it app.error(fn) so that you can easily override it without manually removing one or all or some of the listeners, but at least then it's still "batteries included"

[jonathanong]

something like:

function App() {
  this.on('error', logger);
}

App.prototype.error = function(fn){
  this.removeListener('error', logger);
  this.on('error', fn);
}

function logger(err) {
  if ('test' != this.env) console.error(err.stack);
}

i think that'll work. remember, no .bind(this) necessary in node! haha

[tj]

yeah I think that'll work pretty good, and we can forward mounted app errors upstream

[tj]

think im fine with this for now actually, it's easier to explain app.outputErrors = false than if you call app.error() it overrides it, and you can add additional listeners with "error" etc blha blah. Plus IMHO you always want stderr traces, never know when other forms of reporting may fail

[jonathanong]

haha, so i thought about errors where you don't want them to be logged, but then i realized how much easier error handling will be vs express