The tool works by providing you with a tiny script that you add to your website, to allow all unhandled exceptions to be reported back to JS-Analytics.
JS-Analytics will then provide you with a view of collected errors, count them by browser and allow you to sort the data to provide you with a better overview of what errors has occurred and on which pages the occur.
To use JS-Analytics you login using your Google-login, and then create a project for error collection. On the project page you will be provided with the code you will need to add to your website, and the options you can add to the collection process.
In order for collection to work you will need to have an active PayPal subscription on your project.