getUserMediato read audio, and then the experimental
AudioWorkletNodeAPI to echo it back. As of 2020-04 this API is only implemented in Blink-based browsers: Chrome, Edge, Brave, and Opera.
Headphones are recommended, to avoid feedback. If it makes annoying noises, refresh the page to make it stop.
When ready, press any key. You'll need to give it permission to read from your microphone.