PerformanceNavigationTiming: confidence property

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The confidence read-only property of the PerformanceNavigationTiming interface returns a PerformanceTimingConfidence object containing information that indicates whether the user agent considers returned navigation metrics to be free from external system load unrelated to the page.

For example, if a website has loaded after a browser "cold start" or session restore, its pages may load more slowly as a result. In such cases, a low confidence value would be returned for an associated performance record. On the other hand, if the browser determines a returned performance record to be representative of typical application performance, a high confidence value is returned.

This confidence measure is useful for developers when trying to determine whether a performance issue is a legitimate concern, or an outlier being caused by external factors.

Value

A PerformanceTimingConfidence object.

Examples

Basic usage

This example uses a PerformanceObserver to retrieve confidence data from observed PerformanceNavigationTiming entries. The value property is an enumerated value of low or high, indicating a broad confidence measure, whereas the randomizedTriggerRate property is a number inside the interval 0 to 1 inclusive, representing a percentage value that indicates how often noise is applied when exposing the value.

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    console.log(
      `${entry.name} confidence: ${entry.confidence.value}`,
      `Trigger rate: ${entry.confidence.randomizedTriggerRate}`,
    );
  });
});

observer.observe({ type: "navigation", buffered: true });