# Ecommerce JavaScript Performance > Reduce JavaScript delays by loading only the code each page needs and finding scripts that block customer interaction. - Type: Merchant guide - Level: Intermediate - Reading time: About 6 minutes - Audience: Written for store owners, builders, and designers refining high-performance ecommerce stores. - Last updated: 2026-11-04 - Canonical page: https://academy.getzenbasket.com/merchant-questions/ecommerce-javascript-performance/ - Part of: [Merchant Questions](https://academy.getzenbasket.com/merchant-questions/) on ZenBasket Academy --- ## What you need to know ### How does JavaScript affect ecommerce performance? JavaScript can delay download, parsing, execution and customer interaction, especially on lower-powered phones. It also powers valuable features, so the goal is less and better-timed code rather than removing all JavaScript. ### Why is my ecommerce site using too much JavaScript? A store accumulates too much JavaScript when themes, experiments, apps and tags keep adding bundles without removing old code. Shared code may also load on pages that never use the feature. ### Can JavaScript delay page interaction? Yes. JavaScript runs on the browser's main thread, where long tasks can postpone a tap, input or page update. Split expensive work and avoid recalculating more of the page than the interaction requires. ### What is code splitting? Code splitting divides one large JavaScript bundle into smaller parts that can load by page or feature. A category page should not download checkout code merely because both belong to the same store application. ### What is lazy-loaded JavaScript? Lazy-loaded JavaScript is code fetched or executed only when a page or customer action needs it. For example, a product-video player can wait until the shopper opens the video rather than loading on every page view. ### Should every ecommerce feature load immediately? No. Load essential navigation, product information and buying actions first; defer reviews, recommendations, chat and other optional features until they are needed by the shopper. ### Can unused JavaScript slow down ecommerce sites? Yes. Unused JavaScript still consumes network, parsing, compilation and sometimes execution time. Coverage and bundle-analysis tools can identify code shipped to a page but not used there. ### How do I identify scripts slowing down my store? Record the page with browser performance tools and connect long tasks and network files to their owner or feature. Compare results with a script disabled in a safe test environment before deciding to remove or defer it. ### A quick store check Record every JavaScript file on one product page, its transferred size, execution time, owner, and whether that page needs it. --- ## Frequently asked questions ### Is minifying JavaScript the same as removing it? No. Minification makes code smaller; removing unused code avoids downloading, parsing and running it at all, which is a larger gain. ### Can a small script still cause a large delay? Yes. A small file can run expensive work or repeatedly block the browser's main thread, causing significant interaction delays. --- ## Related learning path - **Ecommerce Image and Video Performance** - **Ecommerce Apps and Third-Party Script Performance** - [ZenBasket Build Guide](https://help.getzenbasket.com/zenbasket-builder/)