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# The Theme JavaScript That Blocked Rendering for 1.2 Seconds
- URL: https://debugly.dev/shopify-theme-javascript-render-blocking/
- Published: 2026-10-09T11:30:00.000Z
- Updated: 2026-10-23T09:13:03.000Z
- Description: One script tag without defer, loading a bundle nothing above the fold needed. How to find what is blocking your paint and what each fix actually changes.
- Author: Rohit Bhadani
- Tags: Shopify, Error Autopsy, Performance, JavaScript

| Change                    | FCP      | LCP      |
| ------------------------- | -------- | -------- |
| Baseline                  | 2,410 ms | 3,890 ms |
| defer on theme bundle     | 1,290 ms | 2,740 ms |
| Section code split out    | 1,180 ms | 2,210 ms |
| Preconnect to app origins | 1,140 ms | 2,050 ms |
| Hero image priority fixed | 1,140 ms | 1,320 ms |

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Related reading: [Tapping a Variant Took 480ms to Do Anything](https://debugly.dev/shopify-inp-variant-selector-main-thread/) explores a connected angle.

Published on [debugly.dev](https://debugly.dev/) by [Rohit Bhadani](https://debugly.dev/about/) | Founder of [Krova Cloud](https://krova.cloud/?ref=debugly.dev)