Lighthouse: Replace large JavaScript libraries with smaller alternatives (deprecated)

Overview

Avoiding large JavaScript libraries can help prevent a large JavaScript payload for your page. This, in turn, reduces the time needed by the browser to download, parse, and execute JavaScript files.

It is always preferable to use smaller yet functionally equivalent JavaScript libraries to prevent a large JavaScript bundle size. Smaller JavaScript bundles can help you avoid a long main-thread blocking time.

How do large JavaScript libraries affect page performance?

Typically, JavaScript bundles on many websites are built using libraries, which are often derived from dependencies i.e., third-party JavaScript code that affects your site functionality.

These dependencies are usually imported onto your page by installing popular JavaScript packages. In many cases, your site functionality may only depend on a few lines of code found in these packages.

However, if the entire package is installed, you may end up with a large JavaScript library, which could mean delivering a large JavaScript payload relative to your intended application.

The larger the JavaScript library, the longer the browser takes to download, parse, and execute JavaScript.

Using smaller alternative libraries can help you optimize your JavaScript payload and delivery for a faster loading page without sacrificing functionality.

How does GTmetrix trigger this audit?

GTmetrix evaluates all the JavaScript libraries on your page and runs them against the Bundle Phobia repository to find out if there are alternative libraries with similar functionality and smaller sizes.

This audit triggers if there is at least one such library.

Clicking the audit reveals the list of alternative libraries you may use in place of your existing large libraries.

How to fix this audit?

It is important to ensure that you're selecting the optimal libraries for your application during your webpage's initial development phase.

You can do so by using the Bundle Phobia tool itself to find a suitable JavaScript package for your application.

Another strategy is to focus on optimizing your dependencies. In many cases, you can achieve significant reductions in JavaScript library size.

Learn more about optimizing your dependencies here.