Flask and Wavesurfer.js audio playback not rendering on HTML

Question

I'm using flask on Python3.7 and trying to add playback functionality. My audio.HTML is rendering fine. However when I try to use the WaveSurfer.js package I get nothing. Do I have an issue in instantiating the wavesurfer instance?

I'm using the dpkg URL via: <script src="https://unpkg.com/wavesurfer.js@7"></script>

I have a 'div' for the content to load: <div id="waveform"> wavesurfer goes here </div>

I think that the below code is where my breakdown is happening. My URL is valid as I've been able to load get playback e.g. HTMLAudio. I was hoping to get some advice one way or another, whether I'm missing something, or on a fool's errand.

{% block scripts %} 
<script>  
var wavesurfer = WaveSurfer.create({
container: document.getElementById('waveform');
waveColor: '#4F4A85';
progressColor: '#383351';
url: "{{ url_for('static', filename=wavdir) }}";
sampleRate: 8789;
});

wavesurfer.on('click', () => {
  wavesurfer.play()
});
</script>
{% endblock %}