The addModule method uses a URL relative to the page URL, so I (the creator) can't simply make the library do:
async function addWorkletHelper(context) {
await context.audioWorklet.addModule("./spessasynth_processor.min.js");
}
This forces us to import the worklet manually.
Copy the spessasynth_processor.min.js from node_modules/spessasynth_lib/dist/ to your destination, for example a public or src folder.
See working with browsers for an automation example.
await context.audioWorklet.addModule(
new URL("./spessasynth_processor.min.js", import.meta.url)
);