Web/API/PerformanceObserver/observe

The observe() method of the PerformanceObserver interface is used to specify the set of performance entry types to observe. The performance entry types are specified as an array of DOMString objects, each naming one entry type; the type names are documented in Performance entry type names in PerformanceEntry.entryType.

When a matching performance entry is recorded, the performance observer's callback function—set when creating the PerformanceObserver—is invoked.

Syntax

observer.observe(options);

Parameters

options

A PerformanceObserverInit dictionary with the following possible members:

entryTypes: An array of DOMString objects, each specifying one performance entry type to observe. May not be used together with the "type" or "buffered" options.
type: A single DOMString specifying exactly one performance entry type to observe. May not be used together with the entryTypes option.
buffered: A Boolean flag to indicate whether buffered entries should be queued into the observer's buffer. Must be used only with the "type" option.

See PerformanceEntry.entryType for a list of valid performance entry type names. Unrecognized types are ignored, though the browser may output a warning message to the console to help developers debug their code. If no valid types are found, observe() has no effect.

Examples

This example creates and configures two PerformanceObservers; one watches for "mark" and "frame" events, and the other watches for "measure" events.

var observer = new PerformanceObserver(function(list, obj) {
  var entries = list.getEntries();
  for (var i=0; i < entries.length; i++) {
    // Process "mark" and "frame" events
  }
});
observer.observe({entryTypes: ["mark", "frame"]});

function perf_observer(list, observer) {
  // Process the "measure" event 
}
var observer2 = new PerformanceObserver(perf_observer);
observer2.observe({entryTypes: ["measure"]});

Specifications

Specification	Status	Comment
Performance Timeline Level 2The definition of 'observe()' in that specification.	Candidate Recommendation	Initial definition of `observe()` method.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`observe`	Chrome Full support 52	Edge Full support ≤79	Firefox Full support 57	IE No support No	Opera Full support 39	Safari Full support 11	WebView Android Full support 52	Chrome Android Full support 52	Firefox Android Full support 57	Opera Android Full support 41	Safari iOS Full support 11	Samsung Internet Android Full support 6.0

Legend

Full support: Full support
No support: No support

PerformanceObserver.observe() by Mozilla Contributors is licensed under CC-BY-SA 2.5.