Web Performance Optimization & Lighthouse · レッスン

Server-Side Rendering（SSR）の影響

Server-Side Rendering（SSR）とClient-Side Rendering（CSR）のパフォーマンス上のトレードオフと、TTIへの影響を評価します。

レッスン 3/411 ステップ

「Server-Side Rendering（SSR）の影響」はCoddyKit上の無料Web Performance Optimization & Lighthouseレッスンです。これはレッスン3/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはWeb Performance Optimization & Lighthouse学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Web Performance Optimization & Lighthouseコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

SSR vs. CSR: The Core Idea

Welcome to understanding how web pages get built! Today, we'll explore two fundamental ways web content reaches your browser: Client-Side Rendering (CSR) and Server-Side Rendering (SSR).

Both have unique impacts on performance, especially how quickly a user can see and interact with your page.

How Client-Side Rendering Works

With CSR, your browser receives a minimal HTML file, often just a blank page with a link to a JavaScript bundle. It's like an empty canvas.

Browser downloads HTML: Very small, quickly.
Browser downloads JavaScript: This is the main part, often large.
JavaScript fetches data & builds UI: After loading, JS executes, calls APIs, and dynamically injects content into the page.

The user sees content only after these steps complete.

CSR Performance & Initial Load

CSR can feel slow initially. The user might see a blank screen or a loading spinner for a noticeable period. This impacts metrics like First Contentful Paint (FCP) and Largest Contentful Paint (LCP).

However, once loaded, subsequent navigation within the app can be very fast, as only data (not full pages) needs to be fetched.

Try this simple CSR example:

<!DOCTYPE html>
<html>
<head>
  <title>CSR Demo</title>
  <style>
    body { font-family: sans-serif; text-align: center; }
    #app { border: 1px solid #ccc; padding: 20px; margin: 20px auto; max-width: 300px; min-height: 50px; }
  </style>
</head>
<body>
  <div id="app"><p>Loading content...</p></div>
  <script>
    document.addEventListener('DOMContentLoaded', () => {
      setTimeout(() => {
        document.getElementById('app').innerHTML = '<h2>Welcome!</h2><p>Content rendered by JS.</p><button>Click Me</button>';
      }, 1000); // Simulate network/processing delay
    });
  </script>
</body>
</html>

How Server-Side Rendering Works

With SSR, the server does the heavy lifting. When a user requests a page, the server processes the request, fetches any necessary data, and constructs the full HTML response.

Browser requests page: Sends request to server.
Server builds HTML: Fetches data, renders the complete page on the server.
Browser receives full HTML: Gets a ready-to-display page.

The user sees content almost immediately as the HTML arrives.

SSR Performance & Initial Load

SSR generally leads to much faster First Contentful Paint (FCP) and Largest Contentful Paint (LCP). Users see meaningful content very quickly, improving perceived performance and SEO.

However, the server must generate the HTML for every request, which can add latency on the server side if not optimized. Let's see an SSR-like output:

<!DOCTYPE html>
<html>
<head>
  <title>SSR Demo</title>
  <style>
    body { font-family: sans-serif; text-align: center; }
    .content { border: 1px solid #ccc; padding: 20px; margin: 20px auto; max-width: 300px; }
  </style>
</head>
<body>
  <div class="content">
    <h2>Welcome!</h2>
    <p>Content rendered directly by the server.</p>
    <button onclick="alert('Hello from SSR!')">Click Me</button>
  </div>
</body>
</html>

Understanding Time To Interactive (TTI)

Time To Interactive (TTI) measures how long it takes for a page to become fully interactive. This means:

The page has displayed useful content (FCP/LCP).
Event handlers are registered for most visible UI elements.
The page responds to user interactions within 50 milliseconds.

TTI is critical because a user can see content but still be unable to click buttons or type into fields if the page isn't interactive.

SSR's TTI Challenge: Hydration

While SSR delivers content quickly, it often sends static HTML. To make this HTML dynamic and interactive, the client-side JavaScript still needs to load and 'take over' the DOM. This process is called hydration.

During hydration, JavaScript attaches event listeners and builds the virtual DOM. If this JS bundle is large, or takes a long time to execute, it can delay TTI even after the content is visible.

Comparing TTI: SSR vs. CSR

The TTI impact differs:

CSR: TTI often aligns closely with FCP/LCP, as all content and interactivity are loaded together. If the JS bundle is small, TTI can be fast.
SSR: FCP/LCP are fast, but TTI can be delayed if hydration is slow. Users might see content but experience a frustrating 'dead zone' where nothing responds.

The goal is to minimize this gap between visible content and interactive content.

Choosing the Right Approach

Deciding between SSR and CSR depends on your project's needs:

SSR is great for: Content-heavy sites (blogs, e-commerce), good SEO, fast initial load for users on slow connections.
CSR is great for: Highly interactive web applications (dashboards, social media feeds), where initial load time is less critical than rich user experience post-load.

Hybrid approaches like Static Site Generation (SSG) or Progressive Hydration also exist to combine benefits.

Quick Check: Rendering Strategies

Based on what we've learned, which statements correctly describe the performance trade-offs between Server-Side Rendering (SSR) and Client-Side Rendering (CSR)?

対話的なレッスンで答える

Recap: SSR, CSR & TTI

In this lesson, we explored Server-Side Rendering (SSR) and Client-Side Rendering (CSR). You learned:

CSR defers rendering to the browser, potentially slowing initial content display but offering dynamic experiences.
SSR renders HTML on the server, providing fast initial content (FCP/LCP) but can delay interactivity (TTI) due to hydration.
Time To Interactive (TTI) is crucial, measuring when a page is fully usable.

Choosing between them involves balancing initial load speed, interactivity needs, and the impact of hydration on TTI.

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よくある質問

「Server-Side Rendering（SSR）の影響」レッスンは無料ですか？

はい。「Server-Side Rendering（SSR）の影響」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Web Performance Optimization & Lighthouseコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Web Performance Optimization & Lighthouseコースには全4レッスンが含まれています。

「Server-Side Rendering（SSR）の影響」で何を学びますか？

Server-Side Rendering（SSR）とClient-Side Rendering（CSR）のパフォーマンス上のトレードオフと、TTIへの影響を評価します。ブラウザで直接実行するハンズオンコードでWeb Performance Optimization & Lighthouseを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Web Performance Optimization & Lighthouseを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのWeb Performance Optimization & Lighthouseは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン3/4です。

「Server-Side Rendering（SSR）の影響」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このWeb Performance Optimization & Lighthouseレッスンでコードを書いて実行できますか？

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