PerformanceResourceTiming: domainLookupEnd property
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2017.
Note: This feature is available in Web Workers.
The domainLookupEnd
read-only property returns the timestamp
immediately after the browser finishes the domain-name lookup for the resource.
If the user agent has the domain information in cache, domainLookupStart
and domainLookupEnd
represent the times when the user agent starts and ends the domain data retrieval from the cache.
Value
The domainLookupEnd
property can have the following values:
- A
DOMHighResTimeStamp
representing the time immediately after the browser finishes the domain name lookup for the resource. 0
if the resource was instantaneously retrieved from a cache.0
if the resource is a cross-origin request and noTiming-Allow-Origin
HTTP response header is used.
Examples
Measuring DNS lookup time
The domainLookupEnd
and domainLookupStart
properties can be used to measure how long it takes for the DNS lookup to happen.
const dns = entry.domainLookupEnd - entry.domainLookupStart;
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 dns = entry.domainLookupEnd - entry.domainLookupStart;
if (dns > 0) {
console.log(`${entry.name}: DNS lookup duration: ${dns}ms`);
}
});
});
observer.observe({ type: "resource", buffered: true });
Example using Performance.getEntriesByType()
, which only shows resource
performance entries present in the browser's performance timeline at the time you call this method:
const resources = performance.getEntriesByType("resource");
resources.forEach((entry) => {
const dns = entry.domainLookupEnd - entry.domainLookupStart;
if (dns > 0) {
console.log(`${entry.name}: DNS lookup duration: ${dns}ms`);
}
});
Cross-origin timing information
If the value of the domainLookupEnd
property is 0
, the resource might be a cross-origin request. To allow seeing cross-origin timing information, the Timing-Allow-Origin
HTTP response header needs to be set.
For example, to allow https://developer.mozilla.org
to see timing resources, the cross-origin resource should send:
Timing-Allow-Origin: https://developer.mozilla.org
Specifications
Specification |
---|
Resource Timing # dom-performanceresourcetiming-domainlookupend |
Browser compatibility
BCD tables only load in the browser