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Speed Medium impact Medium 1–2 h

Less and smaller JavaScript

Large JS delays and burdens the device's CPU.

What it is

JavaScript must be downloaded, parsed, and executed — all of which costs time and performance, especially on weaker mobiles. Large JS bundles worsen interactivity (INP).

Why it matters

JS is the "most expensive" type of resource — unlike an image, the device must also process it. Redundant libraries and unused code create a needless burden.

How to do it

  1. 1Remove unused libraries and code (tree-shaking).
  2. 2Split JS by page (code splitting), load only what's needed.
  3. 3Defer non-critical scripts (defer/async).
  4. 4Consider lighter alternatives to large libraries.

Conclusion

Keep JavaScript to a minimum — every kilobyte is "paid for" twice (transfer + processing). Code splitting and removing dead code help interactivity (INP) the most. This is often the biggest opportunity on modern sites.

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