WorkerGlobalScope: crossOriginIsolated property

Note: This feature is only available in Web Workers.

The crossOriginIsolated read-only property of the WorkerGlobalScope interface returns a boolean value that indicates whether the website is in a cross-origin isolation state. That state mitigates the risk of side-channel attacks and unlocks a few capabilities:

SharedArrayBuffer can be created and sent via a DedicatedWorkerGlobalScope.postMessage() or a MessagePort.postMessage() call.
Performance.now() offers better precision.
Performance.measureUserAgentSpecificMemory() can be accessed.

A website is in a cross-origin isolated state, when the response header Cross-Origin-Opener-Policy has the value same-origin and the Cross-Origin-Embedder-Policy header has the value require-corp or credentialless.

Value

A boolean value.

Examples

const myWorker = new Worker("worker.js");

if (self.crossOriginIsolated) {
  const buffer = new SharedArrayBuffer(16);
  myWorker.postMessage(buffer);
} else {
  const buffer = new ArrayBuffer(16);
  myWorker.postMessage(buffer);
}

Specifications

Specification
HTML Standard # dom-crossoriginisolated-dev

Browser compatibility

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