PerformanceResourceTiming: fetchStart property

The fetchStart read-only property represents a timestamp immediately before the browser starts to fetch the resource.

If there are HTTP redirects, the property returns the time immediately before the user agent starts to fetch the final resource in the redirection.

Unlike many other PerformanceResourceTiming properties, the fetchStart property is available for cross-origin requests without the need of the Timing-Allow-Origin HTTP response header.

Value

A DOMHighResTimeStamp immediately before the browser starts to fetch the resource.

Examples

Measuring time to fetch (without redirects)

The fetchStart and responseEnd properties can be used to measure the overall time it took to fetch the final resource (without redirects). If you want to include redirects, the overall time to fetch is provided in the duration property.

js

const timeToFetch = entry.responseEnd - entry.fetchStart;

Example using a PerformanceObserver, which notifies of new resource performance entries as they are recorded in the browser's performance timeline. Use the buffered option to access entries from before the observer creation.

js

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    const timeToFetch = entry.responseEnd - entry.fetchStart;
    if (timeToFetch > 0) {
      console.log(`${entry.name}: Time to fetch: ${timeToFetch}ms`);
    }
  });
});

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

Example using Performance.getEntriesByType(), which only shows resource performance entries present in the browser's performance timeline at the time you call this method:

js

const resources = performance.getEntriesByType("resource");
resources.forEach((entry) => {
  const timeToFetch = entry.responseEnd - entry.fetchStart;
  if (timeToFetch > 0) {
    console.log(`${entry.name}: Time to fetch: ${timeToFetch}ms`);
  }
});

Specifications

Specification
Resource Timing
# dom-performanceresourcetiming-fetchstart

Browser compatibility

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