js get mic level

/**
 * Create global accessible variables that will be modified later
 */
var audioContext = null;
var meter = null;
var rafID = null;
var mediaStreamSource = null;

// Retrieve AudioContext with all the prefixes of the browsers
window.AudioContext = window.AudioContext || window.webkitAudioContext;

// Get an audio context
audioContext = new AudioContext();

/**
 * Callback triggered if the microphone permission is denied
 */
function onMicrophoneDenied() {
    alert('Stream generation failed.');
}

/**
 * Callback triggered if the access to the microphone is granted
 */
function onMicrophoneGranted(stream) {
    // Create an AudioNode from the stream.
    mediaStreamSource = audioContext.createMediaStreamSource(stream);
    // Create a new volume meter and connect it.
    meter = createAudioMeter(audioContext);
    mediaStreamSource.connect(meter);

    // Trigger callback that shows the level of the "Volume Meter"
    onLevelChange();
}

/**
 * This function is executed repeatedly
 */
function onLevelChange(time) {
    // check if we're currently clipping

    if (meter.checkClipping()) {
        console.warn(meter.volume);
    } else {
        console.log(meter.volume);
    }

    // set up the next callback
    rafID = window.requestAnimationFrame(onLevelChange);
}


// Try to get access to the microphone
try {

    // Retrieve getUserMedia API with all the prefixes of the browsers
    navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia;

    // Ask for an audio input
    navigator.getUserMedia(
        {
            "audio": {
                "mandatory": {
                    "googEchoCancellation": "false",
                    "googAutoGainControl": "false",
                    "googNoiseSuppression": "false",
                    "googHighpassFilter": "false"
                },
                "optional": []
            },
        },
        onMicrophoneGranted,
        onMicrophoneDenied
    );
} catch (e) {
    alert('getUserMedia threw exception :' + e);
}