Class RateTracker

Example

// Initialise it once
const clicks = Trackers.rate(); // or: const clicks = new Trackers.RateTracker();

// Mark when a click happens
document.addEventListener(`click`, () => clicks.mark());

// Compute rate (returned as a number)
clicks.perSecond; // How many clicks per second
clicks.perMinute; // How many clicks per minute
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By default the tracker keeps averaging over all the data it sees. It can be useful to limit it so more accurately tracks changes in frequency.

To do so, pass in options when creating it:

// Eg reset tracker after 5 seconds of inactivity,
// and only keep up to 10 samples max.
const clicks = Trackers.rate({
 sampleLimit: 10,
 timeoutInterval: { secs: 5 }
});
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• timeoutInterval is a makes the tracker reset after some period without mark() being called.
• sampleLimit sets an upper bound for how many of the most recent events should we consider. A smaller value means the analysis will be more responsive to changes in data source, at the cost of jitter. A larger value gets a smoother response, at the cost of responsiveness.

The way it works under-the-hood is we store the timestamp each time mark() is called, and use this as the basis for computation.