Observable JS Apps

Observability isn't just for backends. Client-side javascript applications are the original distributed systems software: real-time, heavily cached, single-paged, asynchronous, multi-domain, with polyglot persistence layers and cascading dependencies and always running massive amounts of JS. So what can we borrow from backend observability practices, in order to better understand our users and how they really experience our applications?  How can we get our finger on the pulse of modern JS apps running in production?

Observability means instrumenting your code so that you can ask any question, whether you anticipated it or not, and understand the internal state of your systems just by observing its outputs. Emily will talk about an event-driven approach to client-side observability for the most complicated parts of Honeycomb's customer-facing React app: the query builder. She will cover instrumentation best practices, what data to collect and why (spoiler alert: high cardinality is queen), and how they use that data to slice and dice and zoom in on some of the strangest unknown-unknowns for real customers. Code examples will be primarily in React or vanilla JS, but takeaways will apply to other popular frameworks. Examples will be in Honeycomb, but context is relevant to distributed tracing and other distsys debugging techniques.