Web applications today are expected to respond instantly. Even minor lags between user action and content load can lead to user drop-off, higher bounce rates, and lost engagement.
At QED42, we’ve been experimenting with several ways to address these challenges, and one technology that has stood out is the Speculation API. This powerful tool has allowed us to solve critical performance bottlenecks, delivering faster and more seamless experiences to our users.
This article breaks down the performance bottlenecks we faced, why traditional methods fell short, and how the Speculation API helped us solve them—both in Vanilla JavaScript and in Next.js 15+ environments.
The problem we solved
Challenge: slow navigation between pages
One of the most common performance issues we faced was slow navigation between pages. In a typical web application, when a user clicks a link, the browser must fetch the new page’s resources, such as HTML, CSS, and JavaScript. This process can take time, especially on slower networks or for pages with heavy assets. The delay between clicking a link and seeing the new page load often led to a poor user experience.
Traditional solutions and their limitations
To address this, we initially relied on traditional techniques like <link rel="prefetch"> and <link rel="preload">. While these methods helped to some extent, they had significant limitations:
The breakthrough: Speculation API
Implementation: how we did it
To demonstrate how we implemented the Speculation API, we’ll walk through examples in both Vanilla JavaScript and Next.js 15+. These examples reflect real-world scenarios where we used the API to solve performance challenges.
Vanilla JavaScript implementation
In one of our projects, we used the Speculation API to preload the next page when a user hovers over a link. Here’s how we did it:
Impact
Next.js 15+ implementation
In a Next.js 15+ project, we used the Speculation API to preload critical pages during the initial page load. Here’s how we implemented it:
Enable the Speculation API in next.config.js:
Add Speculation rules in a component:
Impact
Comparing the Speculation API to alternatives
While the Speculation API has been a game-changer for us, it’s important to understand how it compares to other solutions:
Lessons learned and best practices
Through our experience with the Speculation API, we’ve identified several best practices:
Why the Speculation API matters
The broader landscape of web performance
Web performance optimization is a multi-faceted challenge that involves reducing load times, minimizing resource usage, and improving user experience. Techniques like lazy loading, code splitting, and caching have been widely adopted to address these challenges. However, these methods often require significant effort and can be difficult to implement effectively.
The Speculation API represents a shift towards native, browser-level optimizations. By providing developers with tools to preload resources dynamically, it reduces the need for complex workarounds and enables more efficient performance optimizations.
The future of predictive loading
As web applications become more dynamic and user-centric, the ability to predict and preload resources based on user behaviour will become increasingly important. The Speculation API is a step in this direction, offering a glimpse into the future of web performance optimization.
Compatibility and adoption
While the Speculation API is still in its early stages, it is supported by modern browsers like Chrome and Edge. As adoption grows, we expect to see more widespread use and further enhancements to the API.
Conclusion
The Speculation API has been a transformative tool for us.Enabling dynamic, behaviour-driven preloading, has allowed us to solve critical performance challenges and deliver faster, more seamless experiences to our users.
Whether you’re working with Vanilla JavaScript or Next.js 15+, the Speculation API offers a lightweight and powerful solution to optimize your web application’s performance.
If you’re facing similar performance challenges, we highly recommend exploring the Speculation API. Its ease of use, combined with its powerful capabilities, makes it a valuable addition to any developer’s toolkit.