VREyeParameters

navigator.getVRDisplays().then(function (displays) {
  // If a display is available, use it to present the scene
  vrDisplay = displays[0];
  console.log("Display found");
  // Starting the presentation when the button is clicked:
  //   It can only be called in response to a user gesture
  btn.addEventListener("click", function () {
    vrDisplay.requestPresent([{ source: canvas }]).then(function () {
      console.log("Presenting to WebVR display");

      // Set the canvas size to the size of the vrDisplay viewport

      var leftEye = vrDisplay.getEyeParameters("left");
      var rightEye = vrDisplay.getEyeParameters("right");

      canvas.width = Math.max(leftEye.renderWidth, rightEye.renderWidth) * 2;
      canvas.height = Math.max(leftEye.renderHeight, rightEye.renderHeight);

      drawVRScene();
    });
  });
});