Recs.
Updated
SpecsUpdate
Pros
Pro Automatically captures JavaScript errors
Unlike Airbrake, you don't have to add try/catch blocks to automatically capture JavaScript errors.
Pro Hosted on a CDN already
Unlike Airbrake or LogEntries, you can download the library from GitHub and concatenate/minify it along with your other JS, or you can use it directly from Loggly's CDN.
Cons
Con Timestamps are in UTC in the UI, and can't be converted
Loggly shows all timestamps in UTC, and the bookmarklet that's supposed to convert them to local time doesn't work.
Recommendations
Comments
Out of Date Pros + Cons
Con JS tracker on CDN blocked by ad blockers by default
This means 5%-40% of your users (depending on the demographic) won't send errors.
Hosting the library yourself won't solve the problem, because it makes AJAX requests to loggly.com.
Con No stack traces for JavaScript
Loggly isn't a client-side JS-specific logger, so it doesn't track stack traces. See http://www.slant.co/topics/2615/~what-are-the-best-javascript-client-side-error-logging-services if you need that functionality.