Unfortunately, site is down.
For error tracking I've previously used Sentry [0]. I found it really easy to use and setup in a fairly large JS app. The best part is that it's open source, so you always have the option of hosting it yourself, which removes any fear of vendor lock-in. I'd say it's well worth paying for their SaaS offering.
EDIT: Looking through the docs, it seems they expect you to load their non-versioned third-party sourced script, and it's not even hosted on a CDN. That's a huge security risk, so it's an immediate blacklist for me.