express-useragent

Fast user-agent parser with first-class Express middleware and TypeScript typings. Works server-side in Node.js and in the browser via a lightweight IIFE bundle.

Requires Node.js 18 or newer.

Install

npm install express-useragent

Quick Start

import http from 'node:http';
import { UserAgent } from 'express-useragent';

const server = http.createServer((req, res) => {
  const source = req.headers['user-agent'] ?? 'unknown';
  const parser = new UserAgent().hydrate(source);

  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify(parser.Agent));
});

server.listen(3000);

Express Middleware

ESM usage (Node 18+):

import express from 'express';
import { express as useragent } from 'express-useragent';

const app = express();

app.use(useragent());

app.get('/', (req, res) => {
  res.json({
    browser: req.useragent?.browser,
    os: req.useragent?.os,
  });
});

app.listen(3000);

Alternatively, you can import the whole namespace:

import express from 'express';
import * as useragent from 'express-useragent';

const app = express();

app.use(useragent.express());

app.get('/', (req, res) => {
  res.json({
    browser: req.useragent?.browser,
    os: req.useragent?.os,
  });
});

app.listen(3000);

CommonJS (require) still supports the default export pattern used in older examples:

const express = require('express');
const useragent = require('express-useragent');

const app = express();

app.use(useragent.express());

app.get('/', (req, res) => {
  res.json({
    browser: req.useragent?.browser,
    os: req.useragent?.os,
  });
});

app.listen(3000);

ESM vs CJS at a glance

• ESM (Node 18+):
  • Named import of middleware:

    import { express as useragent } from 'express-useragent';
    app.use(useragent());

  • Namespace import:

    import * as useragent from 'express-useragent';
    app.use(useragent.express());

• CommonJS (require):

  const useragent = require('express-useragent');
  app.use(useragent.express());

Migrating from v1.x to v2.x

• In v1.x, import useragent from 'express-useragent' returned an object with an .express() method used as middleware.
• In v2.x, the default export is a parser instance (for direct parsing). The Express middleware is provided as a named export express (and alias useragentMiddleware). Use one of:
  • import { express as useragent } from 'express-useragent' → app.use(useragent())
  • import * as useragent from 'express-useragent' → app.use(useragent.express())
• CommonJS require('express-useragent').express() continues to work unchanged.

See more end-to-end demos under examples/:

• examples/server.ts — Express middleware demo
• examples/http.ts — raw Node HTTP sample

API Highlights

• new UserAgent() — build a fresh parser instance.
• useragent.parse(source) — quick parse returning the agent snapshot.
• useragent.express() — Express-compatible middleware that hydrates req.useragent and res.locals.useragent.
• parser.Agent — normalized fingerprint with convenience booleans (isMobile, isBot, etc.).

Sample payload:

{
  "isMobile": false,
  "isDesktop": true,
  "isBot": false,
  "browser": "Chrome",
  "version": "118.0.0",
  "os": "macOS Sonoma",
  "platform": "Apple Mac",
  "source": "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_0)..."
}

Browser Usage

The build exports drop-in browser bundles under dist/browser/:

• express-useragent.global.js — readable IIFE that exposes window.UserAgent and window.useragent.
• express-useragent.global.min.js — minified version of the same API.

<script src="/vendor/express-useragent.global.min.js"></script>
<script>
  const agent = new UserAgent().parse(navigator.userAgent);
  console.log(agent.browser, agent.version);
</script>

Prefer consuming the ESM/CJS entry from your bundler when possible:

import { UserAgent } from 'express-useragent';

const agent = new UserAgent().parse(navigator.userAgent);

Scripts

npm install        # install dependencies
npm run lint       # lint the TypeScript sources, tests, and examples
npm run typecheck  # run the TypeScript compiler in noEmit mode
npm test           # execute Vitest (includes adapted legacy suites)
npm run build      # emit dist/ (CJS, ESM, d.ts, browser bundles)

Examples for manual testing:

npm run http      # raw Node HTTP sample
npm run express   # Express middleware demo
npm run simple    # CLI parsing helper

Contributing

Bug reports and PRs are welcome. When submitting changes, please include:

• Updated tests under tests/ covering new parsing behaviour.
• npm test and npm run lint output or reproduction steps.
• Notes in the changelog for breaking updates.

License

MIT © Aleksejs Gordejevs and contributors.