MediaStreamTrack.getConstraints()

The getConstraints() method of the MediaStreamTrack interface returns a MediaTrackConstraints object containing the set of constraints most recently established for the track using a prior call to applyConstraints(). These constraints indicate values and ranges of values that the Web site or application has specified are required or acceptable for the included constrainable properties.

Constraints can be used to ensure that the media meets certain guidelines you prefer. For example, you may prefer high definition video but require that the frame rate be a little low to help keep the data rate low enough not overtax the network. Constraints can also specify ideal and/or acceptable sizes or ranges of sizes. See Capabilities, constraints, and settings for details on how to work with constrainable properties.

A MediaTrackConstraints object which indicates the constrainable properties the Web site or app most recently set using applyConstraints(). The properties in the returned object are listed in the same order as when they were set, and only properties specifically set by the site or app are included.

This example obtains the current constraints for a track, sets the facingMode, and applies the updated constraints.

function switchCameras(track, camera) {
  const constraints = track.getConstraints();
  constraints.facingMode = camera;
  track.applyConstraints(constraints);
}