Tests are currently run only on Chrome and Firefox browsers using a specific version, the ones available in our CI infrastructure.
As the JS client should and must work on more than those 2 browsers, running them on saucelab could ensure that the client is correctly working on latest versions of Chrome, Firefox, IE, Opera, ...
https://saucelabs.com/
https://github.com/karma-runner/karma-sauce-launcher
https://www.npmjs.com/package/browserslist-saucelabs