This script should only be loaded in a browser extension.

[xunziheng]

when I write browser.xxx in content script ui within main world.

it doesn't work. so why, maybe it's not allowed to use browser api in main world content script?

browser.runtime.sendMessage(message).then((response) => {
  console.log('sw response: ', response);
});

[xunziheng]

should I use window.postMessage to messaging between main world and isolated world, then use browser.runtime.sendMessage to messaging between isolated world content script and service work?

[aklinker1]

Main world content scripts don't have access to the web extension APIs, other than external messaging if you set that up.

window.postMessage will work as well.