Google's **Page Speed** is a top-tier ranking factor. When a browser loads a site, the biggest delay is often caused by external **JavaScript files**. These files stop the browser from rendering content until they are fully processed, destroying your Lighthouse score.

This tutorial provides the simplest, most essential fix for webmasters: **Defer Parsing of JavaScript**. By adding the `defer` attribute, you ensure that primary content loads first, leading to a perfect Lighthouse score and immediate SEO benefits.

Diagram Explaining JavaScript Defer Parsing vs Standard Loading


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Why Script Deferral is a Revenue Booster

  • Direct SEO Impact: Google prioritizes sites where the main content loads quickly. Deferring non-essential scripts ensures your LCP score is high.
  • Instant UX Improvement: Users see content faster, reducing frustration and leading to longer sessions (more AdSense views).
  • High Lighthouse Score: This fix directly addresses major warnings in Google's PageSpeed and Lighthouse reports.

The Defer Attribute Implementation Manual

This fix involves adding the defer attribute to external JavaScript files in your theme's HTML.

  1. Access Theme HTML: Go to **Theme (테마)** and click **Edit HTML**.
  2. Locate Script: Search for external script files (e.g., `adsbygoogle.js` or `widget.js`).
  3. Apply Defer (The Crucial Step): Inside the opening <script> tag for that file, insert the word **defer** before the closing bracket.

    Original Script: <script async src=".../adsbygoogle.js">

    Corrected Script: <script async **defer** src=".../adsbygoogle.js">

  4. Repeat for all scripts (e.g., analytics scripts, comment scripts).
  5. Save Changes: Click **Save** and immediately run a Lighthouse test to verify speed improvement.

Conclusion

Deferring JavaScript parsing is a foundational technical optimization. By ensuring your site's core content is prioritized over non-essential scripts, you create a lightning-fast experience that Google rewards with higher search rankings.

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