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Performancemediummetrics

Use secure and up-to-date JS libraries

rule · js-libraries

JavaScript libraries can quickly accumulate and introduce security risks or performance bottlenecks if not managed carefully.

Code Examples

Checking for Vulnerabilities

Shell
# Using npm
npm audit
 
# Using pnpm
pnpm audit
 
# Using yarn
yarn audit

Replacing Heavy Libraries

JavaScript
// ❌ Bad: Importing a heavy library like Moment.js (280KB+)
import moment from 'moment';
console.log(moment().format('MMMM Do YYYY'));
 
// ✅ Good: Using a lightweight alternative like date-fns (modular imports)
import { format } from 'date-fns';
console.log(format(new Date(), 'MMMM do yyyy'));

Why It Matters

  • Security: Outdated libraries are a primary vector for cross-site scripting (XSS) and other attacks.
  • Performance: Many older libraries were designed for a different era and include redundant polyfills or non-tree-shakable code.
  • Maintenance: Keeping dependencies up-to-date simplifies future upgrades and ensures access to the latest features and bug fixes.
  • Bundle Size: Libraries often make up the bulk of a web application's JavaScript; optimizing them has a high impact.

Best Practices

Run npm audit (opens in a new tab) or an equivalent scan before replacing libraries, because the biggest wins usually come from removing one outdated or oversized dependency rather than blindly rotating packages.

✅ Regular Audits: Run npm audit or use tools like Snyk as part of your CI/CD pipeline. ✅ Modular Imports: Choose libraries that support ES Modules and tree-shaking. ✅ Check BundlePhobia: Before adding a new library, check its impact on bundle size. ✅ Native Alternatives: Use native browser APIs (e.g., Intl for formatting, fetch for requests) instead of libraries when possible.

Tools & Validation

Verification

Automated Checks

  • Measure the affected page or flow in Lighthouse, PageSpeed Insights, or DevTools and confirm the targeted metric improves.
  • Inspect the network waterfall or performance timeline to confirm the intended resource or execution change actually took effect.

Manual Checks

  • Verify the change on a throttled mobile profile, not just local desktop.
  • If this rule maps to a budget or Web Vital, confirm the page now stays within that threshold.