Js Libraries

Use secure and up-to-date JS libraries

Outdated or vulnerable libraries pose security risks and often include unnecessary bloat that degrades performance.

Quick Reference

• Regularly audit dependencies for known security vulnerabilities
• Replace heavy libraries with lightweight alternatives (e.g., date-fns vs moment)
• Ensure libraries are properly versioned and served via reliable CDNs or self-hosted

Check

Check the project's JavaScript dependencies for known vulnerabilities and outdated versions.

Fix

Update vulnerable libraries to secure versions and replace bloated dependencies with modern, lightweight alternatives.

Explain

Explain the risks of using outdated JavaScript libraries and the benefits of using lightweight alternatives.

Code Review

Review the routes, assets, and loading behavior that affect Use secure and up-to-date JS libraries. Flag exact files, requests, or rendering steps that add unnecessary network, CPU, or layout cost, and describe the measurement method used to confirm the issue.

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For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/performance/js-libraries

Use secure and up-to-date JS libraries

Detects JavaScript libraries and checks for known vulnerabilities

Priority: medium · Difficulty: intermediate · Time: 10 min

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

Code Examples

#

Checking for Vulnerabilities

# Using npm
npm audit

# Using pnpm
pnpm audit

# Using yarn
yarn audit

Replacing Heavy Libraries

// ❌ Bad: Importing a heavy library like Moment.js (280KB+)

console.log(moment().format('MMMM Do YYYY'));

// ✅ Good: Using a lightweight alternative like date-fns (modular imports)

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• Security: Outdated libraries are a primary vector for cross-site scripting (XSS) and other attacks.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 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

• npm-audit
• Snyk
• BundlePhobia
• Dependabot

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.