Web applications today are dependent on JavaScript to provide dynamic and interactive user experiences. The performance costs associated with all this JavaScript can be considerable. As developers and solution architects design and optimize web applications, understanding how JavaScript impacts loading times and user experience is crucial. In this article, we’ll look at some key things to consider when making your web application perform better, particularly where JavaScript is concerned.
Poorly implemented JavaScript can bring web applications to crawl, resulting in users bouncing away and being frustrated with their experience. Knowing when this code loads and when/how it should be loaded is crucial for maintaining a rich, performant experience. Lazy loading, a technique where JavaScript is only loaded when absolutely necessary, can help alleviate some of these performance pains. All that JavaScript code can still jam up the browser’s main thread, causing the browser to defer user interactions.
In order to deliver truly high performance, developers need to consider a few critical metrics first. Others are Time To First Byte (TTFB), Cumulative Layout Shift (CLS), and Largest Contentful Paint (LCP). Optimizing these metrics is critical for developing fast, smooth web apps that meet strong user demand.
The Impact of JavaScript on Load Times
JavaScript is an incredibly amazing tool, especially for adding a dizzying level of interactivity to web applications and that’s the downside to performance. One of the biggest culprits is that excessive usage of JavaScript can hold up the browser’s critical main thread. When this happens, users are left with long periods without any indication that their input — a click, a scroll — is having an effect.
When a user opens a page, the browser spends considerable time loading, parsing, and executing JavaScript before displaying any interactive content. In the process, this additional delay can ruin the immediate performance experience of the application. In a world of impatient users, developers need to make sure that JavaScript isn’t a drag and so that frustrate users.
Reducing JavaScript code as much as possible is an important step in improving your performance. Tree-shaking and other techniques can help developers remove unused code from their applications. Dev’s can help loading times by tuning the impact of the size of the overall JavaScript payload. This is a logical, seamless user experience.
Strategies for Optimizing JavaScript Loading
One of the best ways to make web applications faster is loading scripts asynchronously or with a deferred loading strategy. By adding async and defer attributes in script tags, developers will stop JavaScript from blocking the rendering of the page. This keeps any HTML content from being blocked, so users can start interacting with your page way faster.
In particular, developers should leverage SSR and/or SSG in conjunction with other optimizations to further reach their performance goals. These techniques, collectively called server-side rendering, help take the load off of your client’s browser by pre-rendering pages on the server side. By serving the user’s requested page as a complete HTML document, SSR and SSG help boost performance and increase time to content.
Hydration is critical to even begin the process of making static HTML interactive. After the webpage loads, JavaScript then “reawakens” the HTML elements so users can interact with them, all while maintaining lightning-fast performance. Grasping this flow is crucial for developers to build apps with incredible performance and highly interactive interfaces.
Monitoring Performance Metrics for Continuous Improvement
As we’ve discussed, performance is first and foremost an architectural choice that directly impacts happiness, loyalty, and engagement of your users. Developers must continuously monitor key performance metrics to identify areas for improvement. TTFB, CLS and LCP are great metrics to help you understand the experience your users are having.
Measuring performance in terms of percentiles can shine a light on those issues that are introducing frustration to our most impacted users. By taking these concerns into consideration, developers have the opportunity to create an experience that even all users will greatly appreciate. Third-party scripts create even more performance headaches. When these scripts are unavoidable, they can slow your web application and cause a poor experience due to inconsistent performance across browsers.
Self-hosting third-party scripts provides a way forward by giving developers more control over loading and caching these scripts. This approach allows you to avoid the undesirable effects caused by most third-party scripts without losing any of the functionality they offer.
