Experts discuss SSR, hydration, partial hydration, and advanced frameworks like Qwik and React Server Components, highlighting how to optimize performance and interactivity.
Episode Description
Experts discuss SSR, hydration, partial hydration, and advanced frameworks like Qwik and React Server Components, highlighting how to optimize performance and interactivity.
Episode Summary
In this extended panel discussion, the JavaScript Jam hosts welcome Dan Shappir—performance tech lead, W3C web performance expert, and JavaScript Jabber panelist—along with special guests including Misko Hevery, the creator of Angular and Qwik. They begin by examining how frameworks evolved from pure client-side rendering to server-side rendering (SSR) and static site generation (SSG), explaining why hydration can degrade interactivity on large pages. The conversation then shifts to partial hydration solutions—like the islands architecture and server components—that selectively load code, improving user experience on lower-end devices. Misko introduces Qwik’s “resumability” approach, eliminating hydration by persisting state across server and client boundaries, and Dan highlights the practical challenges of adopting such new paradigms. The group weighs real-world trade-offs in e-commerce, content sites, and complex apps, underscoring that performance is now a core concern for developers. They end by discussing future metrics like Interaction to Next Paint (INP), which may further incentivize frameworks to reduce CPU and bandwidth usage in order to enhance real-user performance.
Chapters
00:00 – 06:00 | Welcome, Introductions & High-Level Overview
At the outset, the hosts set the tone for an open-mic conversation about all things web development and JavaScript. They introduce Dan Shappir, whose background spans performance-focused roles at Wix and Next Insurance, as well as involvement with the W3C Web Performance Working Group. The group outlines how JavaScript Jam Live encourages audience participation, with anyone from beginners to experts invited to share questions or insights. They briefly mention recurring themes—server-side rendering, hydration, SEO factors, and user engagement—promising a deep dive into new techniques to improve rendering speed and interactivity. This segment emphasizes that performance is no longer an afterthought; it’s front and center, driving the evolution of modern frameworks and developer best practices.
06:00 – 12:00 | The Shift from Client-Side Rendering to SSR
Dan begins describing how the ecosystem moved away from purely client-rendered single-page apps due to poor initial load times and complicated resource fetching. He explains that SSR and static site generation (SSG) arose to address these shortcomings, delivering HTML pre-rendered on the server so that users see content faster. However, the panel highlights that the same app code must still load on the client for interactivity, thus introducing the concept of hydration. This segment delves into how a fully SSR’d page can appear quickly but remain effectively “frozen” until JavaScript attaches event listeners. While it often feels like an improvement over pure client-side apps, hydration can still create large JavaScript bundles and performance bottlenecks on weaker devices.
12:00 – 18:00 | Understanding Hydration’s Hidden Costs
Here, the conversation explores hydration in more depth. Dan points out that rerunning the entire rendering process on the client just to attach event handlers can be expensive, especially on mid-range or low-end mobile devices. He shares real-world horror stories of impatient users rage-clicking buttons before hydration completes, resulting in broken interactions or multiple unintended submissions. This leads to discussion of how frameworks often assume that hydration finishes by the time a user attempts to engage with a page, which simply isn’t true in many realistic scenarios. The participants emphasize that while SSR solved some visibility metrics, it didn’t entirely fix interactivity, spurring new approaches to reduce JavaScript or delay certain scripts.
18:00 – 24:00 | Progressive Hydration & Developer Trade-offs
The topic shifts to progressive hydration, where developers aim to hydrate only the parts of the interface that need interactivity soonest. For example, a server-rendered blog article may not need any client-side wiring until a user scrolls to comments or clicks “Like.” However, this technique can add mental overhead—teams must decide precisely when and how code loads. The guests debate how solutions like Remix and Svelte use built-in fallback behaviors so that a page remains operational even if hydration hasn’t completed. They also note that many frameworks require new APIs or deeper structural changes to break the “long-running hydrate function” into smaller pieces, further complicating how developers reason about data flow and event handling.
24:00 – 30:00 | Islands Architecture: Optimizing Static Content
Next, they examine the islands architecture popularized by Astro, which treats most of a page as purely static while identifying only certain “islands” for dynamic interaction. Dan explains that this method significantly shrinks JavaScript bundles by focusing client-side code solely on active components, such as an image carousel or shopping cart widget. Although it can yield strong performance benefits, the panel warns that it often pairs best with multi-page application (MPA) flows. If developers want single-page transitions or advanced client-side state management, they may need a separate or hybrid routing mechanism. This illustrates a persistent tension between shipping less JavaScript overall and offering rich in-browser experiences.
30:00 – 36:00 | Server Components & React’s Evolving Paradigm
At this juncture, the hosts compare the islands approach with React Server Components (RSC), a newer feature that aims to reduce client bundle size by separating server-only and client-only components. Dan outlines the promise of RSC: purely presentational components remain server-side, never shipping to the browser. However, bridging these server components with interactive client ones introduces complexity. Listeners learn how RSC must differentiate between “use client” and default server-side behaviors, a shift that some developers may struggle with after years of conventional SSR. The panel notes that React’s power can sometimes be overshadowed by growing intricacy, pushing the community to consider alternatives like Svelte, Solid, or new architecture choices within React itself.
36:00 – 42:00 | Qwik and the Concept of Resumability
Misko Hevery joins to discuss Qwik—a new framework built around “resumability” rather than hydration. Instead of re-executing an entire component tree on the client, Qwik persists server-generated state so the UI can continue instantly upon load. The group dives into details: Qwik serializes component boundaries, letting user interactions “resume” from the exact server-rendered state. This approach can drastically reduce the CPU overhead associated with hydration, particularly on mobile. Misko highlights that Qwik effectively merges SSR and client-side code into a single model, as opposed to forcing developers to think about partial hydration or shipping separate bundles. Yet Qwik’s novelty means adoption requires new mental models and a willingness to leave behind older frameworks, a leap not every team will make.
42:00 – 48:00 | Migrating Legacy Apps & Hybrid Approaches
Attendees question how an established React-based e-commerce site might shift to Qwik without complete rewrites. Misko and Dan emphasize incremental migration paths: one strategy involves wrapping certain React components as “islands” within Qwik, or vice versa, so teams can gradually convert. They also point out that any rewrite—framework-based or otherwise—is inherently challenging. Realistically, businesses have to weigh potential performance gains against developer training, code churn, and the risk of regressions. The conversation broadens to the role of tooling and compilers that can refactor or transform existing codebases. Ultimately, the panel acknowledges that, while bridging solutions exist, the simpler path may be to choose the right framework from the start if performance is the top priority.
48:00 – 54:00 | React’s Momentum, Next.js, and the Market Realities
The group addresses React’s immense popularity and the safety net it represents. Even if hydration is suboptimal, many organizations prioritize a robust talent pool and ecosystem. Dan cites Chrome User Experience Report data showing that Next.js sites, despite SSR by default, often score poorly on performance because developers still bundle too much code. This sparks debate on whether advanced solutions like server components or progressive loading can fix systemic issues in React-based projects. They discuss how a large mindshare and steady improvements might keep React dominant for years, yet new options like Qwik and Solid offer glimpses into a possibly faster, more resilient web where interactivity doesn’t demand massive script downloads.
54:00 – 1:00:00 | Developer Experience vs. User Experience
Shifting focus, the hosts contemplate how frameworks must balance DX (developer experience) against real-world performance. While React was lauded for its simple mental model of “re-render on state change,” modern features—like concurrency, suspense boundaries, and server components—make that mental model far more complex. Misko reiterates that Qwik tries to preserve the developer’s intuitive approach while skipping the hydration step. The panel also notes Svelte’s compiler-first philosophy, which some find more straightforward but which hasn’t unseated React. They pose the question: is the industry’s inertia around React too strong, or could new performance requirements—driven by user expectations and metrics—spark a widespread shift toward less JavaScript-heavy solutions?
1:00:00 – 1:06:00 | Core Web Vitals and Why They Matter
In this segment, the discussion turns to how Google’s Core Web Vitals—Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS)—have pressured teams to optimize. Dan explains that SSR improved LCP, but FID can remain misleadingly high if hydration blocks user interactions. They mention that some developers inadvertently “game” FID by deferring or gating features, which hurts real UX. With a potential switch to Interaction to Next Paint (INP), the panel predicts teams will need to adopt more robust solutions to handle real-world input timing. They note that performance is becoming a shared concern across product managers, designers, and engineers, driving more sophisticated frameworks and measurement.
1:06:00 – 1:12:00 | Lighthouse, Synthetic Tests & Field Data
Here, the guests compare lab metrics from Lighthouse—like Time to Interactive (TTI) or Total Blocking Time (TBT)—with actual field data from the Chrome User Experience Report. While Lighthouse can reveal large script bundles or slow transitions in a controlled test, it doesn’t fully capture real usage patterns, device constraints, or user behaviors. The participants warn that a site passing Lighthouse with high scores might still feel sluggish to certain demographics or regions. They underscore that as frameworks adopt partial hydration or resumability, companies need real user monitoring (RUM) to confirm those theoretical gains manifest in practice, rather than just in synthetic benchmarks.
1:12:00 – 1:18:00 | Handling State and Caching in Modern Apps
Transitioning to more technical specifics, the conversation delves into challenges of application state. SSR solutions often push developers to “lift state” to the server, but caching complexities arise when partial updates or offline interactions come into play. The panel explores whether advanced routing solutions or chunked hydration can handle dynamic sections while preserving performance. They debate how frameworks can maintain global state without re-downloading the entire JavaScript bundle on every route change. The notion of smaller, context-specific states emerges as a technique to lighten re-renders. Ultimately, the hosts stress that performance goals must align with the complexity of your app—an ultra-dynamic UI might justify bigger bundles, but many sites simply do not require so much code.
1:18:00 – 1:24:00 | Retrofitting vs. Building from Scratch
In this chapter, Dan and Misko respond to questions about whether it’s easier to rebuild an app in a faster framework or to optimize step-by-step. They acknowledge that organizational politics, developer expertise, and ROI all factor into the decision. While Qwik promises dramatic benefits if you adopt its model fully, some prefer incremental improvements—like code-splitting or microfrontends—that let them keep using React. This nuance underscores that “best” is context-dependent, shaped by how Qwikkly a company needs results and how risk-averse they are. The hosts conclude that no single solution instantly fixes every performance woe; it’s about understanding one’s own codebase and user needs before making big architectural changes.
1:24:00 – 1:30:00 | Emerging Trends & Compiler Optimizations
Here, the guests reflect on how compilers influence the future of the web. They talk about Svelte’s compile-time approach that eliminates a heavy runtime, leading to smaller bundles and improved performance. Dan mentions that React itself may move toward a compiler solution—codenamed “React Forget”—which aims to handle side effects and reactivity more automatically. They debate how far we can push “zero-runtime” concepts, especially once new frameworks or build tools can analyze code for hydration boundaries or partial rendering. While excited about these possibilities, they caution that every new layering of transformation can confuse developers who expect JavaScript to behave consistently. Balancing advanced optimizations with comprehensibility remains a core challenge.
1:30:00 – 1:36:00 | Real-World Performance Wins & Pitfalls
Developers and audience members share anecdotes on the practical impact of performance. In e-commerce, even slight improvements to page responsiveness often yield outsized gains in conversions. Yet many teams discover that performance regressions creep in through unmonitored third-party scripts, large images, or newly added features. The panel stresses the importance of continuous measurement, code reviews for performance, and purposeful architecture decisions—rather than slapping partial hydration on top of an already bloated app. They also highlight that technology alone—be it Next.js, Astro, or Qwik—won’t solve everything unless teams pay attention to best practices around data fetching, caching, and resource loading.
1:36:00 – 1:43:00 | Closing Q&A, Future Directions & Farewell
In the final chapter, the speakers field last-minute questions from listeners, summarizing the major takeaways: hydration can be a performance bottleneck, and new paradigms like islands, server components, or resumability are attempts to overcome it. Each approach carries unique benefits and trade-offs, from developer experience to code maintainability. Misko reiterates that Qwik’s success hinges on developer willingness to rethink SSR and embrace a truly state-resumable model. Dan highlights that, ultimately, successful frameworks and tooling must help developers ship less JavaScript to the client, speeding up real-world interactivity. The episode concludes with thanks to the audience, reminders to subscribe for future events, and a unifying message that the quest for a faster, more user-friendly web continues.