Webmon currently monitors your website from 4 locations and correlate the results to figure out status of your website. However, it doesn't look into JS errors

Webmon currently monitors your website from 4 locations and correlate the results to figure out status of your website. However, it doesn't look into JS errors generated because it doesn't actually render the content. But we are working on a new RUM service which will also include reporting page load errors that the users are seeing. but this is also not fool proof as prior JS errors in the page could have halted the execution of our script.