🇬🇷 CityJS Athens 2025

Hydration, Islands, Streaming, Resumability… Oh My!

Our ecosystem can be overwhelming! First, we had the rise of SSR and SSG, each with its own gigantic pile of frameworks and tools. Then, partial hydration enabled us to hydrate only some of our components on the client, as we've seen in React Server Components.

But what about islands? Do they relate at all to Streaming SSR? Moreover, what is resumability, and why do I keep hearing about it? […] Oh, did anyone say rendering on the Edge?

Well… There are many approaches out there, and all of them argue that their philosophy is best. In this session, we’ll go over these architecture/rendering patterns, to help shed some light on how some are implemented and the concepts behind them.

Transcript

1. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! • MAY 31, 2025. γειά σας, Athens! 👋 🇬🇷
2. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! 🤯 MATHEUS ALBUQUERQUE • @ythecombinator
3. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… MATHEUS ALBUQUERQUE • @ythecombinator LET’S DISCUSS MORE AFTER! OH MY! 🤯
4. Hydration HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
5. “Hydration is the process of attaching behavior to declarative content to make it interactive.” Why Progressive Hydration is Harder than You Think • Miško Hevery, 2022
7. HYDRATION: INNER CHALLENGES ↝ ASSOCIATE DOM ELEMENTS WITH THEIR CORRESPONDING EVENT HANDLERS. ↝ ONCE A USER EVENT TRIGGERS A HANDLER, WE NEED TO UPDATE THE STATE. ↝ ONCE THE STATE UPDATES, THE FRAMEWORK NEEDS TO RECREATE THE COMPONENT HIERARCHY. 🤯
8. HYDRATION: UX CHALLENGES GET HTML DOWNLOAD JS PARSE + EXECUTE JS RECOVER STATE + BIND LISTENERS 🟢 FAST (USUALLY)
9. HYDRATION: UX CHALLENGES GET HTML DOWNLOAD JS PARSE + EXECUTE JS RECOVER STATE + BIND LISTENERS 🔴 SLOW (ON BAD NETWORK CONDITIONS)
10. HYDRATION: UX CHALLENGES GET HTML DOWNLOAD JS PARSE + EXECUTE JS RECOVER STATE + BIND LISTENERS 🔴 SLOW (DEPENDING ON THE DEVICE AND AMOUNT OF JAVASCRIPT)
11. HYDRATION: UX CHALLENGES RECOVER STATE + BIND LISTENERS 🔴 SLOW (DEPENDING ON THE AMOUNT OF DOM NODES TO BE TRAVERSED AND REFERENCES TO BE RE-BOUND TO LISTENERS) GET HTML DOWNLOAD JS PARSE + EXECUTE JS
12. HYDRATION: UX CHALLENGES INITIAL REQUEST HTML ARRIVES VIEW PAINTED JAVASCRIPT ARRIVES JAVASCRIPT IS PARSED — RESUMABILITY, WTF? • RYAN CARNIATO 0
13. HYDRATION: DX CHALLENGES
14. HYDRATION: DX CHALLENGES
16. Islands Architecture 1993 1998 2008 2017 2020 2021 2022 2023 2024 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
18. ISLANDS ARCHITECTURE ↝ SELECTIVELY, PROGRESSIVELY ENHANCING BITS OF SERVER-RENDERED HTML WITH CLIENT-SIDE JS. ↝ SMALL, FOCUSED, CHUNKS OF INTERACTIVITY WITHIN SERVER-RENDERED WEB PAGES. ↝ SINGLE APPLICATION IN CONTROL OF FULL-PAGE RENDERING → MULTIPLE ENTRY POINTS.
19. ISLANDS ARCHITECTURE ↝ THE SCRIPT FOR THE ISLANDS CAN BE DELIVERED AND HYDRATED INDEPENDENTLY, ALLOWING THE REST OF THE PAGE TO BE JUST STATIC HTML. ↝ MORE SPECIFICITY AROUND HOW THE ENHANCEMENT OCCURS.
20. HYDRATION vs. ISLANDS POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE (STATIC HTML) POST CONTENT (STATIC HTML) COMMENTS SOCIAL CTA RENDER ALL COMPONENTS TOGETHER AND HYDRATE. RENDER ALL COMPONENTS, HYDRATE KEY ONES FIRST AND THEN PROGRESSIVELY HYDRATE THE OTHERS. STATIC COMPONENTS ARE SERVER-RENDERED HTML. SCRIPTS ARE REQUIRED ONLY FOR INTERACTIVE ONES. TRADITIONAL HYDRATION PROGRESSIVE HYDRATION ISLANDS
21. HYDRATION vs. ISLANDS POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE (STATIC HTML) POST CONTENT (STATIC HTML) COMMENTS SOCIAL CTA RENDER ALL COMPONENTS TOGETHER AND HYDRATE. RENDER ALL COMPONENTS, HYDRATE KEY ONES FIRST AND THEN PROGRESSIVELY HYDRATE THE OTHERS. STATIC COMPONENTS ARE SERVER-RENDERED HTML. SCRIPTS ARE REQUIRED ONLY FOR INTERACTIVE ONES. TRADITIONAL HYDRATION PROGRESSIVE HYDRATION ISLANDS
22. HYDRATION vs. ISLANDS POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE POST CONTENT COMMENTS SOCIAL CTA POST TITLE (STATIC HTML) POST CONTENT (STATIC HTML) COMMENTS SOCIAL CTA RENDER ALL COMPONENTS TOGETHER AND HYDRATE. RENDER ALL COMPONENTS, HYDRATE KEY ONES FIRST AND THEN PROGRESSIVELY HYDRATE THE OTHERS. STATIC COMPONENTS ARE SERVER-RENDERED HTML. SCRIPTS ARE REQUIRED ONLY FOR INTERACTIVE ONES. TRADITIONAL HYDRATION PROGRESSIVE HYDRATION ISLANDS
23. ISLANDS ARCHITECTURE ↝ STANDALONE: Astro, Qwik, Marko, Iles, Capri. ↝ PREACT: Fresh, preact-island, microsite. ↝ SOLIDJS: Solid Start, isolid. ↝ SVELTE: Elder.js.
25. ISLANDS ARCHITECTURE: MARKO ↝ STREAMING RENDERING + AUTOMATIC PARTIAL HYDRATION + COMPILER. ↝ AUTOMATIC PARTIAL HYDRATION ALLOWS INTERACTIVE COMPONENTS TO HYDRATE THEMSELVES. ↝ HYDRATION CODE IS ONLY SHIPPED FOR INTERACTIVE COMPONENTS. 🤯
27. ISLANDS ARCHITECTURE: ASTRO ↝ BY DEFAULT, SHIPS ZERO JAVASCRIPT. ↝ EVERY ISLAND IS LOADED IN PARALLEL. ↝ MULTI-FRAMEWORK: BUILD ISLANDS WITH REACT, PREACT, SVELTE, VUE, AND OTHERS. ↝ YOU CAN SPECIFY THE LOADING STRATEGY FOR EACH ISLAND INDIVIDUALLY.
28. ISLANDS ARCHITECTURE: ASTRO - - - import MyReactComponent from ' . . /components/MyReactComponent.jsx'; - - - <MyReactComponent />
29. ISLANDS ARCHITECTURE: ASTRO - - - import MyReactComponent from ' . . /components/MyReactComponent.jsx'; - - - <MyComponent client:load /> <MyComponent client:idle /> <MyComponent client:visible /> <MyComponent client:media={string} /> <MyComponent client:only={string} />
30. ISLANDS ARCHITECTURE 🟢 REDUCES THE AMOUNT OF JAVASCRIPT CODE SHIPPED TO THE CLIENT 🟢 FASTER PAGE LOADS AND TIME TO INTERACTIVE (TTI) 🟢 KEY CONTENT IS AVAILABLE ALMOST IMMEDIATELY TO THE USER 🟢 STATIC CONTENT IS RENDERED ON THE SERVER = PAGES ARE SEO-FRIENDLY GREAT 🟡 HIGHLY INTERACTIVE PAGES WOULD PROBABLY REQUIRE THOUSANDS OF ISLANDS NOT GREAT
31. ISLANDS ARCHITECTURE 🟢 REDUCES THE AMOUNT OF JAVASCRIPT CODE SHIPPED TO THE CLIENT 🟢 FASTER PAGE LOADS AND TIME TO INTERACTIVE (TTI) 🟢 KEY CONTENT IS AVAILABLE ALMOST IMMEDIATELY TO THE USER 🟢 STATIC CONTENT IS RENDERED ON THE SERVER = PAGES ARE SEO-FRIENDLY GREAT 🟡 HIGHLY INTERACTIVE PAGES WOULD PROBABLY REQUIRE LOTS OF ISLANDS NOT GREAT
34. Resumability 1993 1998 2008 2017 2020 2021 2022 2023 2024 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
35. #hotTake 🌶 A considerable part of the modern isomorphic landscape is built on top of libraries that weren't initially created for server rendering.
37. #question 🤔 What if frameworks were built on SSR in the fi rst place?
39. OPA LANGUAGE 🤯
42. “Resumability is about pausing execution in the server and resuming execution in the client without having to replay and download all of the application logic.” Resumable vs. Hydration • Qwik documentation website
43. RESUMABILITY ↝ SOME WORK → PAUSE → RESUME. ↝ USE WHAT HAPPENED DURING THE EXECUTION ON THE SERVER AND AVOID EXTRA WORK WHEN THE APPLICATION STARTS IN THE BROWSER. ↝ ATTACHES GLOBAL EVENT HANDLERS AT STARTUP AND THEN ONLY RUNS THE NECESSARY CODE ON INTERACTION.
44. HYDRATION vs. RESUMABILITY ↝ EVENT HANDLER CREATION HAPPENS BEFORE THE EVENT IS TRIGGERED (EAGER) ↝ ALL POSSIBLE EVENT HANDLERS ARE CREATED AND REGISTERED (SPECULATIVE) ↝ CLIENT REDOES WORK ↝ REQUIRES THE FRAMEWORK TO DOWNLOAD AND EXECUTE THE COMPONENTS TO FIGURE OUT HIERARCHY HYDRATION ↝ EVENT HANDLER CREATION HAPPENS AFTER THE EVENT IS TRIGGERED (LAZY) ↝ ONLY TRIGGERED EVENTS ARE CREATED AND REGISTERED (AS-NEEDED) ↝ CLIENT DOESN'T REDO WORK (VIA DESERIALIZATION) ↝ REQUIRES ALL THE INFORMATION TO BE SERIALIZED IN THE HTML RESUMABILITY
45. HYDRATION vs. RESUMABILITY ↝ EVENT HANDLER CREATION HAPPENS BEFORE THE EVENT IS TRIGGERED (EAGER) ↝ ALL POSSIBLE EVENT HANDLERS ARE CREATED AND REGISTERED (SPECULATIVE) ↝ CLIENT REDOES WORK ↝ REQUIRES THE FRAMEWORK TO DOWNLOAD AND EXECUTE THE COMPONENTS TO FIGURE OUT HIERARCHY HYDRATION ↝ EVENT HANDLER CREATION HAPPENS AFTER THE EVENT IS TRIGGERED (LAZY) ↝ ONLY TRIGGERED EVENTS ARE CREATED AND REGISTERED (AS-NEEDED) ↝ CLIENT DOESN'T REDO WORK (VIA DESERIALIZATION) ↝ REQUIRES ALL THE INFORMATION TO BE SERIALIZED IN THE HTML RESUMABILITY
46. RESUMABILITY 🟢 STARTUP PERFORMANCE 🟢 RENDERING PERFORMANCE (ONLY CHANGED COMPONENTS NEED TO BE RE-RENDERED) 🟢 FINE-GRAINED LAZY-LOADING 🟢 PROGRESSIVE INTERACTIVITY GREAT 🟡 *PRELOAD CRITICAL PAGE INTERACTIONS 🟡 THE ONLY OPTION FOR DEVELOPERS TO LEVERAGE RESUMABILITY IS TO USE QWIK 🟡 TOO LITTLE DISCUSSION AVAILABLE ON THE IDEA NOT GREAT
47. RESUMABILITY 🟢 STARTUP PERFORMANCE 🟢 RENDERING PERFORMANCE (ONLY CHANGED COMPONENTS NEED TO BE RE-RENDERED) 🟢 FINE-GRAINED LAZY-LOADING 🟢 PROGRESSIVE INTERACTIVITY GREAT 🟡 PRELOAD CRITICAL PAGE INTERACTIONS* 🟡 THE ONLY* OPTION FOR DEVELOPERS TO LEVERAGE RESUMABILITY IS TO USE QWIK 🟡 TOO LITTLE DISCUSSION AVAILABLE ON THE IDEA NOT GREAT
48. #hotTake 🌶 Qwik is an example of the outside of the box thinking that is sometimes required on the web.
49. RESUMABILITY OUT THERE
50. RESUMABILITY OUT THERE
51. Streaming SSR + Selective Hydration 1993 1998 2008 2017 2020 2021 2022 2023 2024 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
52. #question 🤔 Who here works with React?
55. HYDRATION IN REACT: BEFORE ↝ HYDRATION COULD ONLY BEGIN AFTER THE ENTIRE DATA WAS FETCHED AND RENDERED. ↝ USERS COULDN’T INTERACT WITH THE PAGE UNTIL HYDRATION WAS COMPLETE FOR THE WHOLE PAGE. ↝ PARTS OF YOUR APP THAT LOAD FAST WOULD ALWAYS HAVE TO WAIT FOR THE SLOW ONES.
56. HYDRATION IN REACT: BEFORE FETCHING DATA (SERVER) RENDERING HTML (SERVER) LOADING CODE (CLIENT) HYDRATING TIME TO FIRST BYTE FIRST CONTENTFUL PAINT TIME TO INTERACTIVE
57. HYDRATION IN REACT: AFTER TIME TO FIRST BYTE FIRST CONTENTFUL PAINT TIME TO INTERACTIVE […] FETCHING DATA (SERVER) RENDERING HTML (SERVER) HYDRATING LOADING CODE (CLIENT) […] […] […] […] […] […]
58. HYDRATION IN REACT: AFTER ↝ REACT PRIORITIZES HYDRATING THE PARTS THAT THE USER INTERACTED WITH BEFORE THE REST. ↝ COMPONENTS CAN BECOME INTERACTIVE FASTER BY ALLOWING THE BROWSER TO DO OTHER WORK AT THE SAME TIME AS HYDRATION.
59. HYDRATION IN REACT: AFTER ↝ REACT WON'T WAIT FOR HUGE COMPONENTS TO LOAD TO CONTINUE STREAMING HTML FOR THE REST OF THE PAGE. ↝ WHEN THE HTML BECOMES AVAILABLE ON THE SERVER, IT WILL BE ADDED TO THE SAME STREAM ALONG WITH A SCRIPT TAG AND INSERTED IN THE RIGHT PLACE.
62. HYDRATION STREAMING ISLANDS RESUMABILITY SELECTIVE HYDRATION RSC CSR SSR STATIC RENDERING INCREMENTAL STATIC GENERATION PROGRESSIVE HYDRATION VIEW TRANSITIONS EDGE RENDERING SPA MPA PARTIAL HYDRATION
63. HYDRATION STREAMING ISLANDS RESUMABILITY SELECTIVE HYDRATION RSC CSR SSR STATIC RENDERING INCREMENTAL STATIC GENERATION PROGRESSIVE HYDRATION VIEW TRANSITIONS EDGE RENDERING SPA MPA PARTIAL HYDRATION
64. The Future 🔮 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
65. — ISLANDS & SERVER COMPONENTS & RESUMABILITY, OH MY! • RYAN CARNIATO
66. ROUTING & MPAs vs. SPAs
67. ROUTING & MPAs vs. SPAs WATERFALLS
68. ROUTING & MPAs vs. SPAs HYBRID ROUTING
69. HYDRATION
70. OKB JAVASCRIPT
71. CODE EXTRACTION
73. CODE EXTRACTION: JAXER IN 2008 < ! - - Database, file, and socket access from JavaScript - - > <script runat="server"> var resultSet = Jaxer.DB.execute("SELECT * FROM myTable"); var newPrice = resultSet.rows[0].price; </script> < ! - - Directly call server-side functions from the browser - - > <script runat="server-proxy"> function getPriceFromServer() { return 42; } </script> <button onclick="alert(getPriceFromServer())">Price</button> < ! - - Share validation code on the browser and server - - > <script runat="both"> function validateCreditCard(number) {} </script>
74. < ! - - Database, file, and socket access from JavaScript - - > <script runat="server"> var resultSet = Jaxer.DB.execute("SELECT * FROM myTable"); var newPrice = resultSet.rows[0].price; </script> < ! - - Directly call server-side functions from the browser - - > <script runat="server-proxy"> function getPriceFromServer() { return 42; } </script> <button onclick="alert(getPriceFromServer())">Price</button> < ! - - Share validation code on the browser and server - - > <script runat="both"> function validateCreditCard(number) {} </script> CODE EXTRACTION: JAXER IN 2008
75. CODE EXTRACTION: APP ROUTER IN 2023
76. COMPILERS
78. “So here’s my advice for anyone who wants to make a dent in the future of web development: time to learn how compilers work.” Compilers are the New Frameworks • Tom Dale, 2017
79. INFRASTRUCTURE
80. WHY SOMETHING IS THE FUTURE
81. Closing Thoughts HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
82. THE SOLUTION TO THE PROBLEM ONLY CHANGES THE PROBLEM. #1 of 7 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
83. WHILE SEEN AS COMPETITIVE, A LOT OF THESE ARE ACTUALLY COMPLEMENTARY! #2 of 7 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
84. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / THE SAME PATTERN CAN BE BENEFICIAL AND DETRIMENTAL. IT IS ALSO QUITE LIKELY THAT DIFFERENT TYPES OF PAGES REQUIRE DIFFERENT RENDERING PATTERNS ON THE SAME WEBSITE. #3 of 7
86. APPLICATION HOLOTYPES
87. APPLICATION HOLOTYPES Portfolio Content Storefront Social Network I m m ersive Holotype Personal Blog CNN Amazon Facebook Figma Interactivity Minimal Linked Articles Purchase Multi-Point, Real-time Everything Session Depth Shallow Shallow Shallow - Medium Extended Deep Values Simplicity Discover-ability Load Performance Dynamicism I m m ersiveness Routing Server Server, HTML Swap HTML Swap, Hybrid Hybrid, Client Client Rendering Static Static, SSR Static, SSR SSR CSR Hydration None Progressive, Partial Partial, Resumable Any None (CSR) Frameworks 11ty Astro, Elder Marko, Qwik, Hydrogen Next, Remix Create React App — PATTERNS FOR BUILDING JAVASCRIPT WEBSITES IN 2022, BY RYAN CARNIATO
88. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / #4 of 7
89. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / IT'S EASY TO THINK WE'RE JUST GOING BACK TO RENDERING HTML ON THE SERVER. BUT THESE DAYS THE BOUNDARIES ARE VERY DIFFERENT! #4 of 7
90. CLIENT ⁶ SERVER BOUNDARIES
91. CLIENT ⁶ SERVER BOUNDARIES
92. CLIENT ⁶ SERVER BOUNDARIES
93. CLIENT ⁶ SERVER BOUNDARIES
94. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / SOFTWARE DEVELOPMENT CONTINUALLY GOES THROUGH CYCLES. WHAT’S DIFFERENT NOW? WHAT’S TURNED INTO LOST ART? #5 of 7
95. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
96. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
98. HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / THERE'S NO SILVER BULLET. IDENTIFY YOUR CORE METRICS. ALWAYS TRY TO CORRELATE BUSINESS METRICS WITH PERFORMANCE. #6 of 7
99. A PICTURE IS WORTH A THOUSAND WORDS! #7 of 7 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! /
100. This is me, ten years ago, presenting about Ionic at an iOS developers meetup telling them it'd be the future of mobile development!
101. #7 of 7 HYDRATION, ISLANDS, STREAMING, RESUMABILITY… OH MY! / A PICTURE IS WORTH A THOUSAND WORDS! DON'T ALWAYS TRUST SPECULATIONS AND PREDICTIONS!
102. MATHEUS ALBUQUERQUE ↝ 👨💻 STAFF SWE @ MEDALLIA ↝ ⚛ CHAIR @ REACT SUMMIT NYC ↝ ⚡ GOOGLE DEVELOPER EXPERT ↝ 𝕏 YTHECOMBINATOR
103. THAT’S ALL, FOLKS! ΕΥΧΑΡΙΣΤΏ! 👋 🇬🇷 QUESTIONS? MATHEUS ALBUQUERQUE • @ythecombinator ⬆ ALL THE LINKS!