Impact of HTTP/2 and HTTP/3 on module bundling

Anton Ioffe - November 9th 2023 - 10 minutes read

As web development continues to evolve at a breakneck pace, the underlying protocols that govern our data exchanges have not just been spectators. They've actively reshaped the landscape of JavaScript module bundling, demanding both a departure from old concatenation dogmas and a fresh dive into innovative strategies. In this article, we will navigate the transformative impact of HTTP/2 and HTTP/3 on your approach to JavaScript delivery, probing into their nuanced mechanisms for modern web performance optimization. Join us as we dissect these protocols' implications, explore practical bundling nuances with code samples, and arm you with the advanced knowledge to skirt common pitfalls and refactor your bundling techniques for a sleeker, swifter web experience.

The Evolution of HTTP and Its Influence on Bundling

In the context of HTTP/1.1, the strategy for serving JavaScript was largely defined by the protocol's limitations, primarily the restriction to a single request per connection, which directly contributed to the practice of concatenating scripts into large bundles. This method reduced the number of HTTP requests at the expense of cache efficiency — a single change within a bundle mandated the re-download of the entire, potentially hefty, file. Despite its drawbacks, concatenation was a necessary trade for performance; the overhead of establishing multiple HTTP/1.1 connections would otherwise slow page rendering due to the consequential head-of-line blocking.

Enter HTTP/2, a quantum leap from its predecessor aimed at more efficient use of network resources, which introduced multiplexing, allowing multiple requests over a single connection. This innovation reduced the urgency to bundle files, as multiple resources could be transmitted in parallel without incurring the penalties of head-of-line blocking. HTTP/2 also brought server push, potentially serving files before they're explicitly requested, and header compression via HPACK, alleviating overhead. However, while one might conclude that these features render bundling obsolete, that isn't entirely the case. Optimal use of HTTP/2's multiplexing still points to a moderate approach to bundling, combining related assets to reduce latency and making smart use of caching strategies without reverting to the era of monolithic bundles.

The advent of HTTP/3, and the underlying QUIC transport protocol, provides even more granular control over the delivery of JavaScript modules. Its design further reduces the impact of packet loss — a significant improvement for transporting multiple smaller files. While QUIC streams operate independently within the same connection, a lost packet hampers only a single stream rather than the entire connection, thus exhibiting less disturbance to the overall page load performance when compared to HTTP/2. This enhancement in resilience can lend itself favorably to strategies that serve a balanced number of smaller bundles or even individual modules without the catastrophic latency impact once seen in HTTP/1.1.

Strategizing JavaScript delivery in this modern era calls for a nuanced understanding of these protocol innovations. Concatenation is no longer a one-size-fits-all solution; instead, the focus is on a bespoke balance of grouping assets. The ideal approach tailors the division and delivery of code based on the capabilities of both the server and the client, all the while preserving the cache-ability of assets. It's an intricate dance between maximizing the benefits of the protocols and maintaining the simplicity and effectiveness of the codebase. Think critically about the actual performance gains of refined bundling approaches and don't shy away from profiling and experimenting to discover the optimal strategy for your specific use-case.

Module Bundling in an HTTP/2 World

The shift to HTTP/2 has engendered a re-examination of traditional JavaScript module bundling strategies. Under HTTP/1.1, developers amalgamated scripts to reduce the number of requests, a significant bottleneck given the limits on concurrent connections. With HTTP/2’s multiplexing capability, which allows multiple requests over a single connection, the necessity for such a pattern seems diminished. However, this doesn't spell the end for module concatenation. In practice, a balanced approach emerges as the sweet spot: consolidating related modules into smaller, logical bundles minimizes both the increased latency of numerous small files and the cache invalidation issues of a monolithic bundle.

In an HTTP/2 environment, strategically bundling modules not only reduces the overhead associated with numerous small files but also respects the concurrent stream limitation imposed by servers and browsers alike. For instance, Chrome limits to 256 simultaneous streams, a factor to consider when delineating module boundaries. In code, developers might utilize modern JavaScript's dynamic imports to conditionally load modules, allowing finer control over resource delivery. For example:

// Dynamically importing a module when needed
function loadEditorModule() {
  if (isEditorRoute()) {
      .then(module => {
      .catch(err => {
        console.error('Error loading the editor module', err);

While HTTP/2 facilitates the transfer of multiple smaller files, efficiency doesn't solely derive from the protocol's features but from how developers leverage them against browser behavior and real-world conditions. On one hand, merging files into a few larger bundles mitigates HTTP overhead; on the other hand, unbundling completely can lead to performance degradation due to the sheer number of requests. Therefore, understanding your application's specific resource needs and user patterns through profiling becomes critical in harnessing HTTP/2's capabilities effectively.

Still, developers must navigate the complexity that such optimization introduces. Over bundling can re-introduce the caching inefficiencies of HTTP/1.1, while too granular an approach forfeits HTTP/2 benefits. The challenge compounds with diverse browser capabilities and server configurations. It is an exercise in equilibrium: maximize cachability with minimal bundles needed to achieve optimal load time. In critically assessing the performance gains from any given strategy by empirically measuring load times and resource utilization, a pragmatic bundling practice can be attained:

// Example of a function to load modules based on performance metrics
function loadOptimizedModules() {
  const performanceMetrics = gatherPerformanceMetrics();

  if (performanceMetrics.requiresOptimization) {
      .then(module => {
      .catch(err => {
        console.error('Error loading optimized modules', err);

In conclusion, while HTTP/2 brings a transformative approach to resource delivery, it does not abolish the need for judicious module bundling. Developers must adopt a nuanced strategy that acknowledges the protocol’s strengths yet addresses distinctive application requirements. Is the pursuit of extremities in bundling becoming outdated? Perhaps the future lies in modular architecture that coexists gracefully with HTTP/2’s paradigms.

Strategies in HTTP/3: Leveraging QUIC for Module Optimization

HTTP/3, combined with the QUIC protocol, presents unparalleled advantages for transporting JavaScript modules through its independent multiplexed streams and improved congestion control. QUIC achieves a faster handshake by integrating TLS 1.3 within the protocol, effectively combining what would typically be multiple trips into a single round trip. This efficiency, particularly noticeable on mobile and high-latency networks, directly influences JavaScript delivery strategies. Traditional bundling practices aggregated scripts into one large file to mitigate the overhead of HTTP/1's numerous connections. QUIC's architecture, however, encourages a shift towards more granular loading of modules, allowing numerous small, independent streams to load in parallel without the risk of a single dropped packet delaying the entire bundle.

Consider the following example of leveraging HTTP/3's capabilities with dynamic imports in JavaScript:

// Traditional monolithic bundle loading
import './path/to/largeBundle.js';

// HTTP/3-optimized module loading
if (conditionForFeatureA) {
    import('./path/to/moduleA.js').then(module => {
        // Usage of moduleA
if (conditionForFeatureB) {
    import('./path/to/moduleB.js').then(module => {
        // Usage of moduleB

In this scenario, moduleA.js and moduleB.js can be loaded independently over QUIC's multiplexed streams, utilizing the protocol's capability to continue streaming other modules seamlessly even if one drops a packet. This decreases the perceived latency, as users can interact with the parts of the application that have already loaded, while other parts are still in transit.

However, it is crucial to balance the granularity of module loading with the potential overhead caused by excessive file fragmentation. While QUIC minimizes the overhead of multiple streams, developers must avoid inflating the number of requests to the point of diminishing returns. In contexts with sophisticated cache strategies, consolidating related modules could still prove beneficial from a cache efficiency standpoint. Best practices now involve a delicate trade-off between leveraging QUIC’s ability to efficiently handle multiple streams and respecting cacheability and network conditions to optimize asset delivery.

With QUIC's progressive rollout in major browsers and the gradual adaptation by servers, performance-conscious developers should begin to reassess their module bundling strategies. To accommodate for QUIC and HTTP/3, deployment tactics might include fine-tuned chunk splitting in build tools and serving smaller, cache-optimized bundles that tactically harness the protocol's strengths:

// Webpack optimization configuration for HTTP/3
module.exports = {
    // ...
    optimization: {
        splitChunks: {
            chunks: 'all',
            minSize: 10000,
            maxSize: 25000,
    // ...

By adjusting configurations such as minSize and maxSize, developers can define chunk sizes that are aligned with their performance goals, striking a balance between bundling effectiveness and HTTP/3's multiplexing capabilities. This approach accelerates interactivity and reduces the likelihood of bottlenecks typically associated with larger bundles, particularly when coupled with intelligent prefetching and preloading strategies that can further improve page load times.

Common Pitfalls When Bundling with HTTP/2 and HTTP/3

Common Pitfalls: Over-Bundling in HTTP/2 environments

One prevalent misstep when working with HTTP/2 is the commitment to the HTTP/1.1 paradigm of bundling as much as possible into a single file. While this strategy reduced the number of connections in the era of limited parallelism, it dismisses the benefits of HTTP/2's multiplexing capabilities. In the world of HTTP/2:

// Ineffective: One large, monolithic bundle
import largeBundle from './path/to/largeBundle.js';

// Recommended: Modularized imports
import { moduleA } from './path/to/moduleA.js';
import { moduleB } from './path/to/moduleB.js';

The modular approach above leans on HTTP/2's strength to load resources in parallel, improving cacheability and mitigating the risks of re-fetching large bundles due to small changes.

Misunderstanding Server Push and Preloading

Another common mistake is over-reliance on server push and preload directives without a thorough understanding of their impact. Developers sometimes push all assets deemed necessary without considering the client-side effects, thus congesting the user's bandwidth with non-critical resources. Instead, a more selective server push strategy should be adopted, with clear priority given to critical above-the-fold content that is actually required for the initial page load:

// Ineffective: Indiscriminate server push
Link: </assets/js/moduleA.js>; rel=preload; as=script
Link: </assets/js/nonCriticalModule.js>; rel=preload; as=script

// Recommended: Selective server push
Link: </assets/js/criticalInlineScript.js>; rel=preload; as=script

Granularity Gone Awry in HTTP/3

Migrating to HTTP/3 has encountered pitfalls similar to those in HTTP/2 environments, typically through excessive granularity. With HTTP/3's improved handling of packet loss and its ability to independently manage multiple streams, developers might be tempted to split assets into too many small modules:

// Ineffective: Excessive compartmentalization of resources
import 'moduleA.js';
import 'moduleB.js';
// ... dozens of similar imports

// Recommended: Bundles that align with feature sets or routes
import featureSet from './path/to/featureSetBundle.js';

Optimal bundling with HTTP/3 prioritizes a balance, creating bundles that reflect the application’s architecture without resulting in latency due to over-fragmentation.

Blind Optimization without Measurement

The last, and perhaps the most critical, pitfall is optimizing for HTTP/2 or HTTP/3 without actual performance measurement. Developers may apply bundling strategies based on industry hearsay rather than empirical evidence specific to their use case. The application’s unique traffic patterns, resource sizes, and user behavior should dictate the bundling strategy:

// Ineffective: Arbitrary splitting without measurement
splitChunks: {
  chunks: 'all',
  maxSize: 50000, // Chosen without understanding the context

// Recommended: Performance-based approach
splitChunks: {
  chunks: 'all',
  maxSize: calculateOptimalChunkSize(profileData), // Based on actual profiling

In this example, calculateOptimalChunkSize() would be a hypothetical function that returns the ideal maxSize for chunks after evaluating performance metrics. This data-driven approach ensures that bundling decisions enhance the user experience rather than adhere to potentially outdated best practices.

Refactoring Bundling Practices: Questions and Best Approaches

Developers standing at the frontier of modern web development face the complex task of refactoring bundling practices to align with HTTP/2 and HTTP/3 protocols. With the introduction of these protocols, a key consideration surfaces: How does one achieve optimal modularity without sacrificing the performance gains promised by HTTP/2's multiplexing and HTTP/3's QUIC? In the quest for answers, developers must weigh the merits of breaking down larger, monolithic bundles into fine-grained modules against the risks of overwhelming the network with excessive granularity. Code modularity indeed enhances readability and maintainability, but if each tiny module translates into a separate server request, are we not potentially negating the efficiency these protocols were designed to offer?

Ensuring backward compatibility adds another layer of complexity. In a heterogeneous web ecosystem where not all users have graduated to HTTP/2- or HTTP/3-capable browsers or environments, how should one balance the present against the future? Are we architecting our bundling strategies with a finger constantly on the pulse of evolving infrastructure, or will we opts for a lowest common denominator approach that haphazardly respects the old while tepidly embracing the new? It's a delicate dance between optimizing for cutting-edge performance and maintaining a robust user experience across a spectrum of network conditions and client capabilities.

The granular approach of HTTP/2 and HTTP/3 calls into question the conventional wisdom of bundling itself. What exactly is the right size for a module in this new era? Should developers even strive for a universal bundling strategy, or should they adapt their approach contextually based on the application's domain, the nature of its assets, and its usage patterns? Real-world codebases are rarely uniform, so a one-size-fits-all solution seems myopic. Perhaps the solution lies in a more intelligent, adaptive bundling system, one that not only respects the underlying protocol but also responds dynamically to client-side factors such as device capabilities, network conditions, and user behavior.

In essence, we must ask ourselves if we are bundling for the sake of protocol adherence or if we are being guided by a genuine pursuit to enhance user experience. While HTTP/2 and HTTP/3 offer compelling advancements that seemingly tilt the scales towards unbundled, modular asset delivery, a measured approach respecting the nuances of each use case might reveal a more intricate tapestry of best practices. Is it time to divorce ourselves from the safety of familiar practices and, instead, embrace a tailored strategy influenced equally by empirical performance metrics and by a nuanced understanding of user-centric design? This continues to be the provocative conundrum for seasoned developers navigating the shifting landscape of web performance optimization.


In this article, the impact of HTTP/2 and HTTP/3 on module bundling in modern web development is explored. The article discusses how HTTP/2's multiplexing capabilities have changed the traditional approach to bundling, emphasizing the importance of a balanced approach that combines related modules to reduce latency. It also highlights how HTTP/3 and the QUIC transport protocol provide more granular control over module delivery, allowing for a shift towards smaller, independent bundles. The article raises the challenge of optimizing bundling practices and suggests measuring performance and user behavior to determine the optimal strategy. The reader is prompted to consider how to achieve optimal modularity without sacrificing performance gains and how to balance backward compatibility with future advancements in infrastructure.

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