The connectStart
read-only property returns the timestamp
immediately before the user agent starts establishing the connection to the server to retrieve the resource.
The connectStart
read-only property returns the timestamp
immediately before the user agent starts establishing the connection to the server to retrieve the resource.
The connectStart
property can have the following values:
DOMHighResTimeStamp
immediately before the browser starts to establish the connection to the server to retrieve the resource.0
if the resource was instantaneously retrieved from a cache.0
if the resource is a cross-origin request and no Timing-Allow-Origin
HTTP response header is used.The connectStart
and connectEnd
properties can be used to measure how long it takes for the TCP handshake to happen.
js
const tcp = entry.connectEnd - entry.connectStart;
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 tcp = entry.connectEnd - entry.connectStart; if (tcp > 0) { console.log(`${entry.name}: TCP handshake duration: ${tcp}ms`); } }); }); observer.observe({ type: "resource", buffered: true });
Example using Performance.getEntriesByType()
, which only shows resource
performance entries present in the browser's performance timeline at the time you call this method:
js
const resources = performance.getEntriesByType("resource"); resources.forEach((entry) => { const tcp = entry.connectEnd - entry.connectStart; if (tcp > 0) { console.log(`${entry.name}: TCP handshake duration: ${tcp}ms`); } });
If the value of the connectStart
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:
http
Timing-Allow-Origin: https://developer.mozilla.org
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
connectStart |
43 | 12 | 31 | 10 | 32 | 11 | 43 | 43 | 31 | 32 | 11 | 4.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/PerformanceResourceTiming/connectStart