webextensions-examples/google-userinfo/background/main.js

function notifyUser(user) {
  browser.notifications.create({
    "type": "basic",
    "title": "Google info",
    "message": `Hi ${user.name}`
  });}

function logError(error) {
  console.error(`Error: ${error}`);
}

/**
When the button's clicked:
- get an access token using the identity API
- use it to get the user's info
- show a notification containing some of it
*/
browser.browserAction.onClicked.addListener(() => {
  getAccessToken()
    .then(getUserInfo)
    .then(notifyUser)
    .catch(logError);
});