The VREyeParameters interface of the WebVR API represents all the information required to correctly render a scene for a given eye, including field of view information.
The recommendedFieldOfView read-only property of the VREyeParameters interface describes the recommended field of view for the current eye — ideally based on user calibration.
The renderRect read-only property of the VREyeParameters interface specifies the viewport of a canvas into which visuals for the current eye should be rendered.