Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
The MediaTrackSettings dictionary's volume property is a double-precision floating-point number indicating the volume of the MediaStreamTrack as currently configured, as a value from 0.0 (silence) to 1.0 (maximum supported volume for the device). This lets you determine what value was selected to comply with your specified constraints for this property's value as described in the MediaTrackConstraints.volume property you provided when calling either getUserMedia() or MediaStreamTrack.applyConstraints().
If needed, you can determine whether or not this constraint is supported by checking the value of MediaTrackSupportedConstraints.volume as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will ignore any constraints they're unfamiliar with.