PerformanceObserver: observe() method
The observe()
method of the PerformanceObserver
interface is used to specify the set of performance entry types to observe.
See PerformanceEntry.entryType
for a list of entry types and PerformanceObserver.supportedEntryTypes
for a list of entry types the user agent supports.
When a matching performance entry is recorded, the performance observer's callback function—set when creating the PerformanceObserver
—is invoked.
Syntax
js
observe(options)
Parameters
options
-
An object with the following possible members:
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. durationThreshold
-
A
DOMHighResTimeStamp
defining the threshold forPerformanceEventTiming
entries. Defaults to 104ms and is rounded to the nearest of 8ms. Lowest possible threshold is 16ms. May not be used together with theentryTypes
option. entryTypes
-
An array of string objects, each specifying one performance entry type to observe. May not be used together with the "
type
", "buffered
", or "durationThreshold
" options.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. type
-
A single string specifying exactly one performance entry type to observe. May not be used together with the
entryTypes
option.
Return value
None (undefined
).
Examples
Watching multiple performance entry types
This example creates a PerformanceObserver
and watches for "mark"
and "measure"
entry types as specified by the entryTypes
option given in the observe()
method.
js
const observer = new PerformanceObserver((list, obj) => {
list.getEntries().forEach((entry) => {
// Process "mark" and "measure" events
});
});
observer.observe({ entryTypes: ["mark", "measure"] });
Watching a single performance entry type
The following example retrieves buffered events and subscribes to newer events for resource timing events (PerformanceResourceTiming
) using the buffered
and type
configuration options. Whenever you need to configure the observer to use the buffered
or durationThreshold
option, use type
instead of entryType
. Collecting multiple types of performance entry types will not work otherwise.
js
const observer = new PerformanceObserver((list, obj) => {
list.getEntries().forEach((entry) => {
// Process "resource" events
});
});
observer.observe({ type: "resource", buffered: true });
Specifications
Specification |
---|
Performance Timeline # dom-performanceobserver-observe |
Browser compatibility
BCD tables only load in the browser