1. What is Progressive Hydration?

Progressive Hydration is the process of hydrating a server-rendered page over time, instead of hydrating everything at once

2. How does Progressive Hydration work?

How does progressive hydration work?
  1. First the client sends a get request to the server
  2. the server executes all app logic
  3. in order to render the complete HTML page
  4. which it sends back to the client
  5. the client renders the html page
  6. and sends a request for the javascript bundle with critical components
  7. once it receives the javascript bundle
  8. the client executes all app logic again
  9. so as to hydrate those components
  10. 11. and lazy loads the rest later or on demand

3. What are the Pros and Cons of Progressive Hydration?


  • promotes code-splitting
  • defer unimportant parts of the UI
  • reduce bundle size
    • less code to load and execute -> reduce time between FCP and TTI


  • not suitable for dynamic apps,
    • where hydration of every element is required at the same time
  • execute all app logic twice, once on server and once on client
  • still need to hydrate top down (if single root)
    • hydrating a button halfway down the page may require loading and hydrating a huge chunk of code
  • cannot do out of order hydration
    • hydrate components independently from their parents

4. When should you use Progressive Hydration?

  • when you want to use hydration but don't need to hydrate the whole page at once

Better than hydration for everything, except load everything at once sites

see also Hydration, Partial Hydration, React Server Components and Resumability


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