Understanding the different warning messages from PageSpeed Insights speed report

The first thing you need to know when running Google PageSpeed Insights (a.k.a. Google Lighthouse) is that  it only provides general information. This report cannot identify if a certain code is really necessary or not, and this is especially important if you use third-party apps, as it might consider that the app code is not essential and claim that it could slow down your store.

Having this in mind, we will explain below why our app code may appear in some of the warning messages you can see in Google PageSpeed Insights:

Warning "Remove unused JavaScript"

The report detects our code as "unused code". We can definitely say this is a false positive. Bear in mind our app code must be present in order to be displayed on your product pages and be able to recommend products. 

Just for you to know, we are using a Shopify feature called App Embed Block system which allows Merchants use the theme editor to add, remove, and reorder app blocks at the section level for easy customisation.

Warning "Serve static assets with an efficient cache policy"

Our resources are cached for about 1 minute (app data and preferences) and 1 hour (app script).   

The former is necessary to ensure that the app widget shows the most recent data, and allows you to perform changes in your app preferences, and have all changes reflected quickly.   

The latter is convenient to always have the latest version of our app, ensuring compatibility with the changes in the Shopify platform.

Having a different cache policy would cause more harm than good; for instance, our app would not show the most recent changes in regards to the configuration options you have chosen on the app preferences page. For that reason, a shorter cache period guarantees that the app is working to its fullest potential.

Warning "Reduce JavaScript execution time"

In order to display our app on your store, we need to insert the app JavaScript code. The report detects that our app code is loaded and may recommend removing it because the report does not know what it does. However, our app code is essential to show the app.

Please note that our JavaScript files are compressed, minified, and served from a top world CDN to offer your customers the best possible user experience.

Warning "Defer offscreen images"

This warning is referring to the White Christmas decoration (top, bottom, and falling animation) and the sound control, which can be configured on the app preferences page. If you want to enable any of these options, the images have to be loaded to be displayed in your store.

Warning "Avoid long main-thread tasks"

In order for our app to be displayed and continue working while your customers are browsing your store, it needs to remain active, and this is what the report identifies as a "long task." However, most of the time, our app is doing nothing and consuming no resources, but it must remain loaded to interact with your customers' actions.

Warning "Avoid chaining critical requests"

The reports warn that it has detected several scripts running before all page resources have finished loading. The report does not know if some resources are more important than others, so it displays a generic warning.