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 ofDOMString
objects, each specifying one performance entry type to observe. May not be used together with the "type
" or "buffered
" options.type
: A singleDOMString
specifying exactly one performance entry type to observe. May not be used together with theentryTypes
option.buffered
: ABoolean
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 2 The definition of 'observe()' in that specification. |
Candidate Recommendation | Initial definition of observe() method. |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
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