Web worker importScripts DOMException script failed to load

Question

I'm trying to use importScripts

self.addEventListener('fetch', event => {
  ...
  self.importScripts('idb.js');
  ...
}

to load a library for a service worker for a PWA but keep getting

DOMException: Failed to execute 'importScripts' on 'WorkerGlobalScope': 
    The script at 'http://localhost:3000/idb.js' failed to load.

The script file is there, content type is correct, application/javascript, and I've tried it with text/javascript too. My developer tools network tab shows the request starting and then failing really quickly, not getting a chance to hit the server. The status code is (failed) net::ERR_CONNECTION_REFUSED when over http and (failed) net::ERR_FAILED over https. Any help appreciated

Answer 1

According to https://developers.google.com/web/updates/2018/10/tweaks-to-addAll-importScripts

Prior to Chrome 71, calling importScripts() asynchronously outside of the install handler would work. Starting with Chrome 71, those calls throw a runtime exception (unless the same URL was previously imported in an install handler), matching the behavior in other browsers.

I have to move importScripts to the top level of my file or my install handler and it works