Navigation timing

Navigation timestamps

Figure 1. Navigation timestamps (source).

The document navigation timestamps (in addition to those from Resource Timing) are:

1. startTime: Always 0.
2. unloadEventStart: (if there is a previous document) the timestamp immediately before the current document's unload event handler starts.
3. unloadEventEnd: (if there is a previous document) the timestamp immediately after the current document's unload event handler completes.
4. domInteractive: timestamp when DOM construction is finished and interaction with it from JavaScript is possible.
5. domContentLoadedEventStart: timestamp immediately before the current document's DOMContentLoaded event handler starts.
6. domContentLoadedEventEnd: timestamp immediately after the current document's DOMContentLoaded event handler completes.
7. domComplete: timestamp when the document and all sub-resources have finished loading.
8. loadEventStart: timestamp immediately before the current document's load event handler starts.
9. loadEventEnd: timestamp immediately after the current document's load event handler completes.

Other properties

The PerformanceNavigationTiming interface provides additional properties such as redirectCount returning the number of redirects and type indicating the type of navigation.

Example

The domContentLoadedEventEnd and domContentLoadedEventStart timestamps can be used to measure how long it takes to process the DOMContentLoaded event handler.

This example uses a PerformanceObserver, which notifies the caller about new navigation performance entries as they are recorded in the browser's performance timeline. The example uses the buffered option to access entries that were recorded before the observer was created.

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    const domContentLoadedTime =
      entry.domContentLoadedEventEnd - entry.domContentLoadedEventStart;
    console.log(
      `${entry.name}: DOMContentLoaded processing time: ${domContentLoadedTime}ms`,
    );
  });
});
observer.observe({ type: "navigation", buffered: true });

For more examples, see the property pages in the PerformanceNavigationTiming reference documentation.

See also

• PerformanceNavigationTiming
• PerformanceResourceTiming