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Edge Computing with Cloudflare Workers & Deno · Lesson

Server-Side Rendering at the Edge

Render full-stack pages on the fly at the edge for fast first paint, dynamic content, and SEO-friendly HTML.

Server-Side Rendering at the Edge is a free Edge Computing with Cloudflare Workers & Deno lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Edge Computing with Cloudflare Workers & Deno learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why SSR at the Edge?

Server-Side Rendering (SSR) generates HTML on each request instead of shipping a blank shell to the browser.

Running SSR at the edge means:

  • HTML is built close to the user, low latency
  • Great first paint and SEO
  • Personalized, dynamic content per request

SSR vs Static Sites

Static pages are pre-built and cached, fast but identical for everyone.

SSR builds HTML per request, ideal for content that depends on the user, location, or live data.

Many edge apps mix both.

Returning HTML from a Worker

At its core, SSR is just returning an HTML string with the right content type.

export default {
  async fetch(request) {
    const html = '<!DOCTYPE html><html><body><h1>Hello Edge</h1></body></html>';
    return new Response(html, {
      headers: { 'Content-Type': 'text/html;charset=UTF-8' }
    });
  }
};

Injecting Dynamic Data

Fetch data first, then template it into the HTML before responding.

const user = await env.DB.prepare('SELECT name FROM users WHERE id = ?')
  .bind(id).first();
const html = '<h1>Welcome, ' + escapeHtml(user.name) + '</h1>';

Framework SSR on the Edge

Modern frameworks render to a string on the server. Their edge adapters run this inside a Worker.

import { renderToString } from 'react-dom/server';
import { App } from './App';

const markup = renderToString(App({ user }));

Streaming SSR

Instead of waiting for the whole page, stream HTML as it renders so the browser starts painting sooner.

const { readable, writable } = new TransformStream();
renderToReadableStream(App()).then((s) => s.pipeTo(writable));
return new Response(readable, {
  headers: { 'Content-Type': 'text/html' }
});

Hydration

SSR produces static HTML, then client JS hydrates it to make it interactive.

Send the same data to the client so hydration matches the server output exactly, mismatches cause warnings.

const tag = '<script>window.__DATA__ = ' + JSON.stringify(data) + ';</script>';

Using HTMLRewriter

Cloudflare's HTMLRewriter streams and transforms HTML efficiently, perfect for injecting content into a base template.

return new HTMLRewriter()
  .on('title', { element(e) { e.setInnerContent('My Page'); } })
  .transform(response);

Caching SSR Output

Pure-static portions of SSR output can be cached, but personalized pages must not be cached publicly.

Use Cache-Control wisely and vary by user where needed.

headers.set('Cache-Control', 'private, no-store');

SEO Benefits

Because SSR returns fully-formed HTML, crawlers see real content immediately, no JS execution required, improving SEO and social previews.

Best Practices Summary

For solid edge SSR:

  • Fetch data, then render to a string or stream
  • Always escape interpolated data
  • Hydrate with matching client data
  • Stream for faster first paint
  • Cache static parts, never cache private pages publicly

Quick Check

What is the main advantage of streaming SSR over rendering the full page first?

Recap

You can now render full pages at the edge:

  • Return dynamic, escaped HTML per request
  • Use framework adapters and streaming for speed
  • Hydrate with matching client data
  • Transform output with HTMLRewriter and cache carefully

Edge SSR gives you fast, dynamic, SEO-friendly full-stack apps.

Frequently asked questions

Is the “Server-Side Rendering at the Edge” lesson free?

Yes — the full text of “Server-Side Rendering at the Edge” is free to read here on the web, and the Edge Computing with Cloudflare Workers & Deno course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Edge Computing with Cloudflare Workers & Deno course, upgrade to CoddyKit PRO.

What will I learn in “Server-Side Rendering at the Edge”?

Render full-stack pages on the fly at the edge for fast first paint, dynamic content, and SEO-friendly HTML. You practise Edge Computing with Cloudflare Workers & Deno with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Edge Computing with Cloudflare Workers & Deno?

No prior experience is required. Edge Computing with Cloudflare Workers & Deno on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Server-Side Rendering at the Edge” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Edge Computing with Cloudflare Workers & Deno lesson?

Yes. Every Edge Computing with Cloudflare Workers & Deno lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Workers Sites & Pages
  2. Frontend Framework Integration
  3. Database Proxies with Deno
  4. Server-Side Rendering at the Edge
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