What is the most convenient way to stop an Ajax-object in prototype from swallowing exceptions?

Question

Consider this code:

new Ajax.Request('?service=example', {
    parameters : {tags : 'exceptions'},
    onSuccess : this.dataReceived.bind(this)
});

If an exception occurs anywhere in the dataReceived-function when it is called by the Ajax-object, it is swallowed by some exception handling code and the whole process then silently terminates. No exceptions are ever thrown to the browser and it is a bit tedious to debug (for understandable reasons). Is there any straightforward way to prevent this from happening?

Answer 1

I think you can include an onException callback handler with the request options:

new Ajax.Request('?service=example', {
  parameters : {tags : 'exceptions'},
  onSuccess : this.dataReceived.bind(this),
  onException : function(request, ex) { // react somehow }
});

To do it on a global level, the callback handler can be registered with the Ajax.Responders object:

Ajax.Responders.register({
  onException: function(request, ex) {
    // react somehow
  }
});

The first argument will be the Ajax.Request object that triggered the callback.

P.S./FYI: Your exception is being concealed by this code in the Prototype source:

dispatchException: function(exception) {
  (this.options.onException || Prototype.emptyFunction)(this, exception);
  Ajax.Responders.dispatch('onException', this, exception);
}