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Get Started Free →Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize JavaScript bundle size. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.
| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-09 | ✗→✓ | ▲ Improved | -18% | 0% |
| case-01 | ✗→✓ | ▲ Improved | -7% | 0% |
| case-02 | ✗→✓ | ▲ Improved | -35% | 0% |
| case-17 | ✗→✓ | ▲ Improved | -43% | 0% |
| case-03 | ✓→✓ | ＝ Same ✓ | 20% | 0% |
Excessive JavaScript increases parse and execution time, especially on low-end devices, leading to sluggish user experiences and high data costs.
Review the JavaScript bundle sizes and identify any files exceeding 200KB (Gzip/Brotli).
Implement code-splitting, tree-shaking, and dependency audits to reduce the size of the JavaScript bundles.
Explain how large JavaScript files impact the main thread and delay user interactivity (FID/TTI).
Review the routes, assets, and loading behavior that affect Optimize JavaScript bundle size. 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.
For full implementation details, code examples, and framework-specific guidance, see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/performance/js-file-size
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