js-runtime-environment

Get where your JavaScript runs.
Universal runtime detection for modern JS: Browser, Web Worker, Service Worker, Worklet, Node.js, Node.js Worker, Bun, Deno, Electron (main / renderer), NW.js, React-Native, Vercel Edge, Cloudflare Workers, and more — with a single tiny dependency-free module.

Why

JavaScript today runs in many different contexts: sometimes in the browser, sometimes in a Node.js server, sometimes inside a worker, and increasingly in edge environments like Cloudflare Workers or Vercel Edge.

Often the same codebase needs to run in more than one place, but with slight differences in behavior — for example:

• Load different modules depending on server vs. browser.
• Use fs in Node but fall back to fetch in the browser.
• Register event listeners differently in a Service Worker vs. a Web Worker.

js-runtime-environment makes this trivial: you can safely detect the exact runtime and branch your logic without hacks, UA sniffing, or brittle feature checks.

Highlights

• Feature detection, not UA sniffing. Safe try/catch guards to avoid ReferenceError across exotic runtimes.
• Broad coverage. Distinguishes Service/Web/Worklet; detects Node main vs worker threads; recognizes Edge runtimes and desktop shells.
• Drop-in API. Flat, top-level detection functions (isBrowser(), isNode(), …) plus a rich run_env object for advanced logic.
• UMD / CJS. Works everywhere the same way. No configuration required.
• Zero deps. Small footprint, fast, and side-effect free.

What it detects

| Category | Detected environments | | -------------------- | -------------------------------------------------------------------- | | Browsers | Browser (window+document), JsDom | | Workers | Web Worker, Service Worker, Worklet, Dedicated Worker, Shared Worker | | Server runtimes | Node.js, Node.js Worker, Bun, Deno | | Desktop shells | Electron (main / renderer), NW.js | | Mobile / Hybrid | React-Native | | Edge runtimes | Vercel Edge, Cloudflare Workers | | OS (best-effort) | macOS, Windows, Linux, iOS, Android | | Other | Generic shell fallback |

Examples

Node.js

npm i js-runtime-environment

const env = require('js-runtime-environment');
console.log(env.run_env.name); // e.g. "node"

Browser (direct script tag)

<script src="js-runtime-environment.js"></script>
<script>
  console.log(run_env.name);    // "browser"
  console.log(isBrowser());     // true
  console.log(isNode());        // false
</script>

Web Worker

// worker.js
importScripts('js-runtime-environment.js');

postMessage({
  name: run_env.name,          // "web-worker" or "service-worker"
  isWebWorker: isWebWorker()
});

API

run_env (flags & details)

A structured snapshot computed at load time, plus a normalized name.

run_env = {
  name: string,
  web: boolean,
  window: boolean,
  worker: boolean,
  web_worker: boolean,
  service_worker: boolean,
  worklet: boolean,
  nodejs: boolean,
  bun: boolean,
  deno: boolean,
  electron: boolean,
  electron_main: boolean,
  electron_renderer: boolean,
  nwjs: boolean,
  node_main: boolean,
  node_worker: boolean,
  react_native: boolean,
  edge_runtime: boolean,
  cloudflare_worker: boolean,
  shell: boolean,
  details: {
    node: string|null,
    bun: string|null,
    deno: string|null,
    electron: string|null,
    edge: string|null
  }
}

Flat detection helpers

All functions return a boolean and are safe across runtimes.

isBrowser()
isNode()
isBun()
isDeno()
isElectron()
isJsDom()

// Workers
isWebWorker()
isDedicatedWorker()
isSharedWorker()
isServiceWorker()

// OS (best-effort)
isMacOs()
isWindows()
isLinux()
isIos()
isAndroid()

How it works (brief)

• Emphasizes feature detection (e.g., skipWaiting/clients for Service Workers; importScripts for Web Workers; WorkletGlobalScope for Worklets).
• Node.js main vs worker via worker_threads.isMainThread when available.
• Electron via process.versions.electron and window presence to split main/renderer.
• Edge runtimes and platforms use stable globals (e.g., EdgeRuntime, WebSocketPair, HTMLRewriter).
• OS checks combine navigator.userAgentData.platform, navigator.platform, userAgent, and process.platform when present.

Comparison with other libraries

| Feature / Runtime | js-runtime-environment | environment | wherearewe | runtimey | js-runtime | | ------------------- | ------------ | ----------- | ---------- | -------- | ---------- | | Browser | 🟩 | 🟩 | 🟩 | 🟩 | ⬜ | | JsDom | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Web Worker | 🟩 | 🟩 | 🟩 | 🟩 | ⬜ | | Service Worker | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Worklet | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | Node.js | 🟩 | 🟩 | 🟩 | 🟩 | 🟩 | | Node.js Worker | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | Bun | 🟩 | 🟩 | 🟩 | 🟩 | 🟩 | | Deno | 🟩 | 🟩 | ⬜ | 🟩 | 🟩 | | Electron (main) | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Electron (renderer) | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | NW.js | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | React Native | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | Vercel Edge Runtime | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | Cloudflare Workers | 🟩 | ⬜ | ⬜ | ⬜ | ⬜ | | macOS | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Windows | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Linux | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | iOS | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ | | Android | 🟩 | 🟩 | ⬜ | ⬜ | ⬜ |

✅ js-runtime-environment offers the broadest coverage, splitting Node.js main/worker and Electron main/renderer, while also detecting modern edge runtimes, mobile shells, and OS platforms.

Contributing

Issues and PRs are welcome. Useful areas:

• Additional edge-platform detectors.
• More smoke tests across browsers (incl. SW / WW / Worklet).
• Accuracy refinements for React-Native and desktop shells.

License

MIT