chrome-extension

# Chrome extension (Manifest V3) An MV3 extension is **three isolated JavaScript contexts that never share memory and only talk via messages**: 1. **Service worker** (`background.service_worker`) — the logic and lifecycle brain. Ephemeral: Chrome kills it when idle and restarts it on the next event. It has no DOM and no `window`. 2. **Content scripts** — run inside a web page, can read/write that page's DOM, live in an isolated JS world by default. No access to most `chrome.*` APIs except messaging and `storage`. 3. **UI surfaces** — popup (`action.default_popup`), options page, side panel. Normal web pages that load and unload as the user opens/closes them. Internalize that picture first. Most extension bugs are someone treating one of these as if it shared state with another. They do not. The wire between them is `chrome.runtime` messaging and `chrome.storage`. Manifest V3 is the only version the Chrome Web Store accepts; MV2 phase-out began June 2024 and is still rolling out. Build MV3 from the start. ## Pick a skeleton | Setup | Pick when | Cost | |---|---|---| | **Vanilla** (raw files, `load unpacked`) | tiny extension, no npm imports, you want the fastest possible reload loop | no TS, no HMR, manual reloads | | **Vite + CRXJS** (`@crxjs/vite-plugin`) | TS, npm imports, React/Vue popup, you want HMR | a build step; you ship `dist/`, not the repo | Default to **Vite + CRXJS** the moment you want TypeScript or a framework popup — it does the manifest wiring and HMR ...