Once a year we let our imagination go wild for a whole week during our annual Hackweek event. It’s where we come up with product updates, like dark mode support, design them and implement prototypes. The mobile engineering team came up with the idea for a Sentry mobile app that focuses on Release Health. We wanted to give developers a concise but comprehensive view of if a release was healthy, errored, or experiencing abnormal crash sessions across multiple projects.

Here at Sentry, we like to dogfood our product as much as possible. Sometimes, it results in unusual applications of our product and sometimes these unusual applications pay off in a meaningful way. In this blog post, we’ll examine one such case where we use the Sentry JavaScript SDK to instrument Jest (which runs our frontend test suite) and how we addressed the issues that we found.

Transactions are sent when your service receives a request and sends a response, like an API call or a page load. Within each transaction is a series of operations. We built Operations Breakdown to help you, the developer, quickly see how much time was spent in each operation within a transaction. Why? Simple, so you can address the operations with the longest duration and likely causing annoying performance issues for your customer.

What makes JavaScript great is also what makes it frustrating to debug. Its asynchronous nature makes it easy to manipulate the DOM in response to user events, but it also makes it difficult to locate problems. And JavaScript’s ubiquity has resulted in a variety of runtimes (e.g. Chromium’s V8, Safari’s JavaScriptCore, and Firefox’s SpiderMonkey) but having so many platforms can cause dizzying idiosyncracies — all of which need to be supported equally.