Google has updated their mobile-friendly testing tools and their rich results testing tool to work with sites built in JavaScript. Those tools can now both now shows the screenshots for JS based sites, rendered DOM, show JavaScript errors and stacktraces as seen by the Googlebot's web render service. The tools will show rendered HTML, the console log, exceptions, and stack traces.
Here is a screen shot of it in action from Google:
Google also suggests you watch their session at I/O today named Deliver search-friendly JavaScript-powered websites given by John Mueller and Tom Greenaway.
Forum discussion at Twitter.
