General

• Document ready: document.addEventListener("DOMContentLoaded", function(event) { /* do work */ });

ECMA2020

• a?.b optional chaining short for (a !== null && typeof a != "undefined") ? a.b : undefined or (a && a.b) ? a.b : undefined
• a ?? 'default' short for (a !== null && typeof a != "undefined") ? a : 'default'

Promises

Philosophy:

• (en) https://softwareengineering.stackexchange.com/questions/337385/is-rejecting-a-promise-only-for-error-cases (Archive)

Web Extensions

• Chrome browser polyfill: https://github.com/mozilla/webextension-polyfill
  • https://github.com/mozilla/webextension-polyfill/issues/228