PressureObserver: observe() method

{{APIRef("Compute Pressure API")}}{{SeeCompatTable}}{{AvailableInWorkers("window_and_worker_except_service")}}{{securecontext_header}}

The observe() method of the {{domxref("PressureObserver")}} interface tells the pressure observer to start observing pressure changes. After this method is called, the observer will call its callback function when a pressure record for the specified source is observed.

When a matching {{domxref("PressureRecord")}} is obtained, the pressure observer's callback function is invoked.

Syntax

js-nolint

observe(source)
observe(source, options)

Parameters

source
- : A string specifying which {{domxref("PressureRecord.source", "source")}} to observe. See {{domxref("PressureRecord.source")}} for a list of sources and {{domxref("PressureObserver.knownSources_static", "PressureObserver.knownSources")}} for a list of sources the user agent supports.
options {{optional_inline}}
- : An object to configure observation with the following properties:
  - sampleInterval {{optional_inline}}
    - : A number representing the requested sampling interval expressed in milliseconds. Defaults to 0 meaning it will get updates as fast as the system can handle it.

Return value

A {{jsxref("Promise")}} that fulfils with {{jsxref("undefined")}}.

Exceptions

NotAllowedError {{domxref("DOMException")}}
- : Thrown if the Compute Pressure API is disallowed by a {{httpheader('Permissions-Policy/compute-pressure','compute-pressure')}} Permissions Policy.
NotSupportedError {{domxref("DOMException")}}
- : Thrown if the source parameter is not one of the supported sources for this user agent.

Examples

Log current pressure

This example creates a {{domxref("PressureObserver")}} and takes action whenever there is a pressure change. The sample interval is set to 1000ms, meaning that there will be updates at most every second.

function callback(records) {
  const lastRecord = records[records.length - 1];
  console.log(`Current pressure ${lastRecord.state}`);
  if (lastRecord.state === "critical") {
    // disable video feeds
  } else if (lastRecord.state === "serious") {
    // disable video filter effects
  } else {
    // enable all video feeds and filter effects
  }
}

try {
  const observer = new PressureObserver(callback);
  await observer.observe("cpu", {
    sampleInterval: 1000, // 1000ms
  });
} catch (error) {
  // report error setting up the observer
}