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Speed

Scripts take too long to start up

What this means for your business

The JavaScript on your page takes a long time to start up and parse. This is often caused by loading many large scripts at once. The result is a page that looks ready but doesn't respond to clicks for several extra seconds.

How to fix it
Hard
2–4 hours

  1. 1Script bootup time measures how long the browser spends downloading, parsing, and executing all JavaScript at startup. High bootup time means your page sits frozen even though it looks ready.
  2. 2The fastest fix: audit every plugin, app, and third-party script on your site. Each adds JavaScript the browser must process before your page is interactive. Remove anything you don't actively need.
  3. 3Run your page through PageSpeed Insights (pagespeed.web.dev) — under "Diagnostics", look for "Reduce JavaScript execution time". It lists the specific scripts taking the longest.
  4. 4Ask your developer to add defer or async to non-critical scripts so they don't run at startup — they load in the background after your page is visible.
  5. 5If you're loading a large JavaScript library (jQuery, Bootstrap, Lodash) for just one or two features, ask your developer whether a lighter alternative could replace it.

On WordPress

Use WP Rocket's "Delay JavaScript Execution" feature or the Perfmatters plugin. Both delay non-critical JavaScript until the user first interacts with the page — this alone can cut bootup time dramatically without changing your site's functionality.

On Shopify

Install the free Shopify Theme Inspector Chrome extension (search "Shopify Theme Inspector" in the Chrome Web Store). It shows a flame graph of exactly which scripts run on each page and how long each takes — use it to identify the culprits before making changes.

Pro tip: Third-party scripts (chat widgets, review platforms, pixel trackers) are almost always the biggest contributors to bootup time. Try disabling them all temporarily and running PageSpeed Insights — you'll see immediately how much faster your site is without them.

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