PressureRecord: source property

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

The read-only source property is a string indicating the origin source from which the record is coming.


A string indicating the origin source from which the record is coming. The current version of the Compute Pressure API specification supports two main source types:

  • "thermals" represents the global thermal state of the entire system.
  • "cpu" represents the average pressure of the central processing unit (CPU) across all its cores. This state can be affected by other apps and sites than the observing site.

Use the static PressureObserver.knownSources hint to see which source types are supported by your browser. Note that availability can also vary by your operating system and your hardware. Call observe() and check for a NotSupportedError to see if pressure observation is possible.


Using the source property

In the following example we log the value of the source property in the pressure observer callback.

function callback(records) {
  const lastRecord = records[records.length - 1];
  console.log(`Current pressure source: ${lastRecord.source}`);

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


Compute Pressure Level 1
# dom-pressurerecord-source

Browser compatibility

BCD tables only load in the browser