Your pages load JavaScript code that never runs. This still slows down your site for every visitor because the browser has to download and process it before anything else can happen. Think of it like making every customer walk through a storeroom to get to the shop floor.
On WordPress
Use the Asset CleanUp or Perfmatters plugin to disable specific scripts on pages that don't need them. For example, disabling WooCommerce scripts on non-shop pages can remove significant unused JavaScript.
On Shopify
Go through your installed apps and uninstall any you're not actively using — each app adds JavaScript even if you're not using its features. For scripts you keep, use the Shopify Theme Inspector to identify which ones are largest.
Pro tip: Installed-but-unused plugins and apps are almost always the main source of unused JavaScript. A site with 20 plugins is typically loading code for all 20 on every page, even pages that only use 3 of them.
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