I have a set of React components that render live telemetry: an attitude indicator, a moving map, tapes and gauges, a scrolling event log. They take a data source, subscribe to it, and paint whatever numbers arrive. That works for a live feed. The obvious next thing you want is replay: load a recorded session, scrub a timeline, watch the same instruments play it back.
The naive version of this is a trap, and it took me a wrong turn to see why. My first instinct was that replay is a data problem, load the samples, push them into the components in order, done. It compiled, it ran, and the charts were empty. Not broken, not erroring. Empty. The instruments that show a single current value worked fine. The time-series charts sat blank while correct data flowed into them. That empty chart is the whole story of this post, because the reason it's empty is the reason replay is more interesting than it looks.
The components are watching a clock you forgot about
Here's the data source interface these components consume. It's small on purpose:
interface TelemetryValue {
