The future of commerce is dynamic, contextual, and personalized. Hydrogen is a React-based framework for building custom and creative storefronts giving developers everything they need to start fast, build fast, and deliver the best personalized and dynamic buyer experiences powered by Shopify’s platform and APIs. We’ve built and designed Hydrogen to meet the three needs of commerce:
- fast user experience: fast loading and responsive
- best-in-class merchant capabilities: personalized, contextual, and dynamic commerce
- great developer experience: easy, maintainable, and fun.
These objectives have inherent tension that’s important to acknowledge. You can achieve fast loading through static generation and edge delivery, but you must forgo or make personalization a client-side concern that results in a deferred display of critical content. Vice versa, rendering dynamic responses from the server implies a slower initial render but, when done correctly, can deliver better commerce and shopping experience. However, delivering efficient streaming server-side rendering for React-powered storefronts, and smart server and client caching, is a non-trivial and unsolved developer experience hurdle for most teams.
Hydrogen is built and optimized to power personalized, contextual, and dynamic commerce. Fast and efficient server-side rendering with high-performance storefront data access is the prerequisite for such experiences. To optimize the user experience, we leverage a collection of strategies that work together:
- streaming server-side rendering for fast first render powered by React’s Suspense
- React Server Components for efficient, post-render component-level state updates
- built-in server and client data fetching primitives with smart cache defaults
- flexible page and subrequest cache policies to power dynamic and edge delivery.
There’s a lot to unpack here, let’s take a closer look at each one.
Streaming Server-side Rendering
Consider a product page that contains a significant amount of buyer personalized content: a localized description and price for a given product, a dynamic list of recommended products powered by purchase and navigation history, a custom call to action (CTA) or promotion banner, and the assignment to one or several multivariate A/B tests.
A client-side strategy would, likely, result in a fast render of an empty product page skeleton, with a series of post-render, browser-initiated fetches to retrieve and render the required content. These client-initiated roundtrips quickly add up to a subpar user experience.
The client-side rendering (CSR) strategy typically results in a delayed display of critical page content—that is, slow LCP. An alternative strategy is to server-side render (SSR)—fetch the data on the server and return it in the response—that helps eliminate RTTs and allows first and largest contentful paints to fire close together, but at a cost of a slow time-to-first-byte (TTFB) because the server is blocked on the data. This is where and why streaming SSR is a critical optimization.
Hydrogen adopts the new React 18 alpha streaming SSR API powered by Suspense that unlocks critical performance benefits:
- Fast TTFB: the browser streams the HTML page shell without blocking the server-side data fetch. This is in contrast to “standard” SSR where TTFB is blocked until all data queries are resolved.
- Progressive hydration: as server-side data fetches are resolved, the data is streamed within the HTML response, and the React runtime progressively hydrates the state of each component, all without extra client round trips or blocking on rendering the full component tree. This also means that individual components can show custom loading states as the page is streamed and constructed by the browser.
The ability to stream and progressively hydrate and render the application unlocks fast TTFB and eliminates the client-side waterfall of CSR—it’s a perfect fit for the world of dynamic and high-performance commerce.
React Server Components
“Server Components allow developers to build apps that span the server and client, combining the rich interactivity of client-side apps with the improved performance of traditional server rendering.”
—RFC: React Server Components
Server components are another building block that we believe (and have been collaborating on with the React core team) is critical to delivering high-performance storefronts. RSC enables separation of concerns between client and server logic and components that enables a host downstream benefits:
- server-only code that has zero impact on bundle size and reduces bundle sizes
- server-side access to custom and private server-side data sources
- seamless integration and well-defined protocol for server+client components
- streaming rendering and progressive hydration
- subtree and component-level updates that preserve client-state
- server and client code sharing where appropriate.
Server components are a new building block for most React developers and have a learning curve, but, after working with them for the last ten months, we’re confident in the architecture and performance benefits that they unlock. If you haven’t already, we encourage you to read the RFC, watch the overview video, and dive into Hydrogen docs on RSC.
Efficient Data Fetching, Colocation, and Caching
Delivering fast server-side responses requires fast and efficient first party (Shopify) and third party data access. When deployed on Oxygen—a distributed, Shopify hosted V8 Isolate-powered worker runtime—the Hydrogen server components query the Storefront API with localhost speed: store data is colocated and milliseconds away. For third party fetches, the runtime exposes standard Fetch API enhanced with smart cache defaults and configurable caching strategies:
- smart default caching policy: key generation and cache TTLs
- ability to override and customize cache keys, TTLs, and caching policies
- built-in support for asynchronous data refresh via stale-while-revalidate.
Combining the Best of Dynamic and Edge Serving
Adopting Hydrogen doesn’t mean all data must be fetched from the server. On the contrary, it’s good practice to defer or lazyload non-critical content from the client. Below the fold or non-critical content can be loaded on the client using regular React patterns and browser APIs, for example, through use of IntersectionObserver to determine when content is on or soon to be on screen and loaded on demand.
Similarly, there’s no requirement that all requests are server-rendered. Pages and subrequests with static or infrequently updated content can be served from the edge. Hydrogen is built to give developers the flexibility to deliver the critical personalized and contextual content, rendered by the server, with the best possible performance while still giving you full access to the power of client-side fetching and interactivity of any React application.
The important consideration isn’t which architecture to adopt, but when you should be using server-side rendering, client-side fetching, and edge delivery to provide the best commerce experience—a decision that can be made at a page and component level.
For example, an about or a marketing page that’s typically static can and should be safely cached, served directly from the CDN edge, and asynchronously revalidated with the help of a stale-while-revalidate strategy. The opt-in to edge serving is a few keystrokes away for any response on a Hydrogen storefront. This capability, combined with granular and optimized subrequest—powered by the fetch API we covered above—caching gives full control over data freshness and the revalidation strategy.
Putting It All Together
Delivering a high-performance, dynamic, contextual, and personalized commerce experience requires layers of optimizations at each layer of the stack. Historically, this has been the domain of a few, well-resourced engineering teams. The goal of Hydrogen and Oxygen is to level the playing field:
- the framework abstracts all the streaming
- the components are tuned to speak to Shopify APIs
- the Oxygen runtime colocates and distributes rendering around the globe.
Adopting Hydrogen and Oxygen should, we hope, enable developers to focus on building amazing commerce experiences, instead of the undifferentiated technology plumbing and production operations to power a modern and resilient storefront.
Ilya Grigorik is a Principal Engineer at Shopify and author of High Performance Browser Networking (O'Reilly), on a mission to supercharge commerce and empower entrepreneurs around the world.
Wherever you are, your next journey starts here! If building systems from the ground up to solve real-world problems interests you, our Engineering blog has stories about other challenges we have encountered. Intrigued? Visit our Engineering career page to find out about our open positions and learn about Digital by Default.