Document.pointerLockElement

The read-only pointerLockElement property of the Document interface provides the element set as the target for mouse events while the pointer is locked. It is null if lock is pending, pointer is unlocked, or the target is in another document.

An Element or null.

Determine if a canvas element is currently pointer locked.

if (document.pointerLockElement === canvasElement) {
  console.log('The pointer lock status is now locked');
  // Do something useful in response
} else {
  console.log('The pointer lock status is now unlocked');
  // Do something useful in response
}

• Document.exitPointerLock()
• Element.requestPointerLock()
• Pointer Lock