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Benchmarking the New Front End: How to Quantify Single Page App Performance

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It’s easy to quantify page load time in traditional web apps — there are great services for data collection (Google Analytics, New Relic), comprehensive APIs for slicing it up (Navigation Timing), and even static analysis tools (YSLow, Page Speed Insights, Web Page Test). But as web interactions increasingly load content asynchronously and more application functionality moves to the client, quantitatively understanding your users’ experiences becomes a lot more difficult.

Time-to-window-load isn’t relevant anymore. To benchmark our performance progress we needed to collect new events that correspond to when customers can use different components of the page. In practical terms, the new benchmark is when you remove the loading spinner — but here be dragons. We want to know when we remove all the spinners. Feature by feature, on all the pages. For all of our users.

So we want RUM, real user monitoring. We think it’s the best way to have a real-world metric that you can use to understand your users’ experience. We’ll talk about the custom aggregator that we built to slice up some of this data, but we’ll also talk about how you can adapt familiar tools to get some of this data right now. We’ll end with a short discussion of where these tools still don’t meet our needs, and where we hope they’ll go next.

Photo of Rachel Myers

Rachel Myers


Rachel Myers is a Ruby Engineer at ModCloth and an active member of the Ruby on Rails community. She’s passionate about helping others learn to code, and is a teacher and organizer for RailsBridge, a San Francisco-based organization that leads programming workshops for women and minorities. In her spare time, she loves making weird furniture, drinking Scotch, and playing with Legos.

Photo of Emily Nakashima

Emily Nakashima


Emily Nakashima is a UI Engineer and Team Lead at ModCloth. She spends her spare time trying to stuff design skills into developers, and developer skills into other, non-developer people. She’s a primary contributor to the RailsBridge Front End Curriculum and a RailsBridge volunteer. She also likes to make furniture and sneak up on her coworkers from behind while they’re concentrating.


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