Add option to ignore errors thrown during window.unload events

[dmiddlecamp]

We get a ton of exception noise in our logs that we don't have much control over. After some research, I think I've discovered a great chunk of this originates in window.unload.

If we could pass the arguments from the erroring function to processException, or if we had a preProcessException function, we could tag the exception with the event type. This would let us filter out garbage from window.unload events. I did a basic version of this in our Raven build, and we've seen a good drop so far.

I'd like to do this without modifying Tracekit, but here's what I changed on my end so far. I could do some more work on a proper patch, but I wanted to see if anyone had other thoughts.

TraceKit.wrap = function traceKitWrapper(func) {
    function wrapped() {
        try {
            return func.apply(this, arguments);
        } catch (e) {
            if (e) { e._eventType = (arguments && arguments[0]) ? arguments[0].type : null; }
            TraceKit.report(e);
            throw e;
        }
    }
    return wrapped;
};

and then modify window.onerror in Raven with something like:

if (lastException && (lastException._eventType == "unload")) {
    return false;
}

Obviously this wouldn't be a great addition to the project as is, but has anyone else seen similar results?

[mattrobenolt]

@dmiddlecamp Would you mind submitting a pull request for this? We already vendorize and hack up TraceKit anyways, so feel free to modify that.

[benvinegar]

This should be possible using shouldSendCallback. Something like:

var unloadOccurred = false;
window.onbeforeunload = function () {
  unloadOccurred = true;
}

Raven.config('YOUR DSN', {
  shouldSendCallback: function () { 
    return !unloadOccurred; 
  }
}).install();

See Configuration in the docs for more.