摄像头切换

        button.addEventListener('click', function (ev) {
                    console.log(mediaDevice.deviceId)
                    if (typeof currentStream !== 'undefined') {
                        stopMediaTracks(currentStream);
                    }
                    const videoConstraints = {};
                    console.log(mediaDevice.deviceId )
                    videoConstraints.deviceId = { exact: mediaDevice.deviceId };
                    const constraints = {
                        video: videoConstraints,
                        audio: true
                    };
                    navigator.mediaDevices
                        .getUserMedia(constraints)
                        .then(stream => {
                            currentStream = stream;
                            video.srcObject = stream;
                            return navigator.mediaDevices.enumerateDevices();
                        })
                        .then(gotDevices)
                        .catch(error => {
                            console.error(error);
                        });
                })