> https://www.webrtc-experiment.com/DetectRTC/

如果用户没有允许网络摄像头和/或麦克风,则媒体设备的“label”属性将具有“NULL”值.以上页面将显示此消息：“请调用getUserMedia一次”.

PS.您可以在Chrome控制台开发人员工具中输入“DetectRTC.MediaDevices”.

注意：它仅适用于Chrome. Firefox还不支持类似的API. (更新：Firefox支持)

于2015年12月16日更新

注意：以下代码段在Chrome和Firefox中都可用.

if (navigator.mediaDevices && navigator.mediaDevices.enumerateDevices) {
    // Firefox 38+ seems having support of enumerateDevicesx
    navigator.enumerateDevices = function(callback) {
        navigator.mediaDevices.enumerateDevices().then(callback);
    };
}

var MediaDevices = [];
var isHTTPs = location.protocol === 'https:';
var canEnumerate = false;

if (typeof MediaStreamTrack !== 'undefined' && 'getSources' in MediaStreamTrack) {
    canEnumerate = true;
} else if (navigator.mediaDevices && !!navigator.mediaDevices.enumerateDevices) {
    canEnumerate = true;
}

var hasMicrophone = false;
var hasSpeakers = false;
var hasWebcam = false;

var isMicrophoneAlreadyCaptured = false;
var isWebcamAlreadyCaptured = false;

function checkDeviceSupport(callback) {
    if (!canEnumerate) {
        return;
    }

    if (!navigator.enumerateDevices && window.MediaStreamTrack && window.MediaStreamTrack.getSources) {
        navigator.enumerateDevices = window.MediaStreamTrack.getSources.bind(window.MediaStreamTrack);
    }

    if (!navigator.enumerateDevices && navigator.enumerateDevices) {
        navigator.enumerateDevices = navigator.enumerateDevices.bind(navigator);
    }

    if (!navigator.enumerateDevices) {
        if (callback) {
            callback();
        }
        return;
    }

    MediaDevices = [];
    navigator.enumerateDevices(function(devices) {
        devices.forEach(function(_device) {
            var device = {};
            for (var d in _device) {
                device[d] = _device[d];
            }

            if (device.kind === 'audio') {
                device.kind = 'audioinput';
            }

            if (device.kind === 'video') {
                device.kind = 'videoinput';
            }

            var skip;
            MediaDevices.forEach(function(d) {
                if (d.id === device.id && d.kind === device.kind) {
                    skip = true;
                }
            });

            if (skip) {
                return;
            }

            if (!device.deviceId) {
                device.deviceId = device.id;
            }

            if (!device.id) {
                device.id = device.deviceId;
            }

            if (!device.label) {
                device.label = 'Please invoke getUserMedia once.';
                if (!isHTTPs) {
                    device.label = 'HTTPs is required to get label of this ' + device.kind + ' device.';
                }
            } else {
                if (device.kind === 'videoinput' && !isWebcamAlreadyCaptured) {
                    isWebcamAlreadyCaptured = true;
                }

                if (device.kind === 'audioinput' && !isMicrophoneAlreadyCaptured) {
                    isMicrophoneAlreadyCaptured = true;
                }
            }

            if (device.kind === 'audioinput') {
                hasMicrophone = true;
            }

            if (device.kind === 'audiooutput') {
                hasSpeakers = true;
            }

            if (device.kind === 'videoinput') {
                hasWebcam = true;
            }

            // there is no 'videoouput' in the spec.

            MediaDevices.push(device);
        });

        if (callback) {
            callback();
        }
    });
}

// check for microphone/camera support!
checkDeviceSupport(function() {
    document.write('hasWebCam: ',hasWebcam,'<br>');
    document.write('hasMicrophone: ',hasMicrophone,'<br>');
    document.write('isMicrophoneAlreadyCaptured: ',isMicrophoneAlreadyCaptured,'<br>');
    document.write('isWebcamAlreadyCaptured: ',isWebcamAlreadyCaptured,'<br>');
});