const audio = document.querySelector('audio'); // There should be at least ONE <audio> element in your HTML
const button = document.querySelector('button'); // Used to stop the recording

navigator.mediaDevices.getUserMedia({video: false, audio: true})
    .then((stream) => {
        let chunks = []
        let mediaRecorder = new MediaRecorder(stream);  
        mediaRecorder.start()

        button.onclick = () => {
            mediaRecorder.stop();        
        }

        mediaRecorder.onstop = (e) => {
            myBlob = new Blob(chunks, { 'type' : 'audio/ogg; codecs=opus' });
            audio.src = URL.createObjectURL(myBlob);  // The audio's blob will be converted to a url
            // And the audio's source will be the recorded blob
            audio.play();
        }

        mediaRecorder.ondataavailable = (e) => {
            chunks.push(e.data);
        }
})