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.
A DOMHighResTimeStamp
immediately before the browser starts to fetch the resource.
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.
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.
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: ${timeToFetch}ms`);
}
});
});
observer.observe({ type: "resource", buffered: true });
Example using Performance.getEntriesByType()
, which only shows resource
performance entries present in the browser's performance timeline at the time you call this method:
const resources = performance.getEntriesByType("resource");
resources.forEach((entry) => {
const timeToFetch = entry.responseEnd - entry.fetchStart;
if (timeToFetch > 0) {
console.log(`${entry.name}: Time to fetch: ${timeToFetch}ms`);
}
});