how to test lazy loading

Lazy loading is a technique used to improve the performance of web pages that contain large amounts of content such as images, videos or other resources that are not immediately visible to the user. Lazy loading loads these elements only when they become visible to the user in the viewport instead of loading all the elements at the same time. This technique not only reduces the loading time but also the amount of data transferred over the network, thereby improving the user experience.

How to test lazy loading?

Testing lazy loading can be challenging because it involves testing the loading of resources in a dynamic environment. The traditional approach to testing web pages involves loading the entire page and measuring the time taken to load everything, including the lazy loaded elements. However, this approach does not account for the benefits of lazy loading. Below are some of the ways to test lazy loading.

Manual testing using a browser

One way to test lazy loading is by using a browser and manually scrolling through a page to check if the elements are loading correctly. To do this, we need to open the browser’s console and enable the network tab. As we scroll through the page, we can observe the network tab and see if the elements are loading as expected. We can also check the image placeholders, which should not be visible until the images are fully loaded.

Automated testing using headless browsers

We can also use headless browsers like Puppeteer or Selenium to automate the testing of lazy loading. The advantage of using a headless browser is that we can simulate user interactions using scripts and test multiple scenarios quickly. In this way, we can test if all the lazy loaded elements are loading correctly, both in terms of functionality and performance.

Testing using browser extensions

Another way to test lazy loading is by using browser extensions like Lazy Load Test, which is available for Chrome. This extension tests if lazy loading is implemented correctly by measuring the loading time and the number of requests made by the browser. It generates a report that shows the amount of time taken to load the page and the amount of data transferred, including the lazy loaded elements.

Conclusion

Lazy loading is an effective technique for improving the performance of web pages. Testing lazy loading can be challenging due to the dynamic nature of web pages, but with the right tools and techniques, it can be done efficiently. Manual testing using a browser and automated testing using headless browsers are two methods that can help test lazy loading effectively. Using browser extensions can also be a useful way to test lazy loading. By testing lazy loading, we can ensure that our users have a fast and efficient experience that helps them consume our content more easily.