<script>
    async function checkDeviceKind(kind)
    {
        try {
            let devices = await navigator.mediaDevices.enumerateDevices();
            for (let device of devices) {
                if (device.kind === kind)
                    return true;
            }
        } catch (e) {
        }
        return false;
    }

    async function checkSpeakerSelection()
    {
        // Speakers are currently only exposed after getUserMedia.
        try {
            await navigator.mediaDevices.getUserMedia({ audio : true });
        } catch (e) {
        }
        try {
            await navigator.mediaDevices.getUserMedia({ video : true });
        } catch (e) {
        }
        return checkDeviceKind('audiooutput');
    }

    async function enumerate()
    {
        let visible = [];
        if (await checkDeviceKind('videoinput'))
            visible.push('camera');
        if (await checkDeviceKind('audioinput'))
            visible.push('microphone');
        if (await checkSpeakerSelection())
            visible.push('speakerselection');
 
        visible = visible.join('+');
        parent.postMessage(visible, '*');
        result.innerHTML = 'result: "' + visible + '"';
    }

    window.addEventListener("message", enumerate);
</script>

<div id='result'></div>