processAudioBlobURLinBase64.js

/**
 * Apply a callback on audio data provided as a blob data url ("blob:http://...")
 * `processAudioBlobURLinBase64(audio.src, (b64) => console.log(b64));`
 */
function processAudioBlobURLinBase64(audioBlobURL, callback) {
    fetch(audio.src).then((a) => a.blob().then(
        (blob) => {
            var reader = new FileReader();
            reader.readAsDataURL(blob);
            reader.onloadend = function () {
                var base64data = reader.result;
                callback(base64data);
            }
        }
    ))
}