Web Performance Optimization & Lighthouse · 강의

속도를 위한 콘텐츠 우선순위 지정

`async`, `defer`, 리소스 힌트와 같은 기법을 구현하여 중요한 콘텐츠의 우선순위를 정하고 체감 성능을 개선합니다.

속도를 위한 콘텐츠 우선순위 지정은(는) CoddyKit의 무료 Web Performance Optimization & Lighthouse 강의입니다. 이것은 4개 중 3번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 Web Performance Optimization & Lighthouse 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. Web Performance Optimization & Lighthouse 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Why Prioritize Content?

When a browser loads a webpage, it follows a sequence of steps to render content. This is often called the Critical Rendering Path (CRP).

Optimizing the CRP means delivering the most important content to the user as quickly as possible. This improves perceived performance – how fast a user *feels* the page is loading.

Blocking Scripts Slow Down

By default, when the browser encounters a <script> tag, it pauses parsing the HTML, fetches the script, executes it, and then resumes parsing. This is called a render-blocking script.

This can significantly delay how quickly users see content, especially if the script is large or on a slow network.

<html>
<head>
  <title>Blocking Script</title>
  <script>
    // This script blocks HTML parsing
    console.log("Blocking script started.");
    // Simulate a long task
    let start = performance.now();
    while (performance.now() - start < 700) { /* busy wait */ }
    console.log("Blocking script finished.");
  </script>
</head>
<body>
  <h1>Page Content</h1>
  <p>This content appears <b>after</b> the script finishes.</p>
</body>
</html>

Introducing `defer`

The defer attribute tells the browser to download the script in the background without blocking HTML parsing. Once the HTML is fully parsed, the deferred scripts execute in the order they appear in the document.

Non-blocking: HTML parsing continues.
Order preserved: Scripts execute in source order.
Execution time: After HTML parsing, before DOMContentLoaded.

`defer` in Action

Using defer is ideal for scripts that depend on the DOM being fully available, like analytics or UI initialization logic.

See how the 'Page Content' appears before the deferred script executes in the console.

<html>
<head>
  <title>Deferred Script Example</title>
  <script defer>
    console.log("Deferred script 1 started.");
  </script>
  <script defer>
    // This script will run after script 1
    console.log("Deferred script 2 started.");
  </script>
</head>
<body>
  <h1>Page Content</h1>
  <p>This content appears immediately while scripts are downloading.</p>
  <script>
    console.log("HTML parsing complete.");
  </script>
</body>
</html>

Introducing `async`

The async attribute also tells the browser to download the script in the background. However, async scripts execute as soon as they are downloaded, potentially before HTML parsing is complete.

Non-blocking: HTML parsing continues.
Order NOT preserved: Scripts execute as soon as they're ready.
Execution time: Asynchronously, as soon as possible.

`async` vs. `defer`

Choosing between async and defer depends on your script's needs:

Use async for independent scripts (e.g., third-party ads, tracking) where execution order doesn't matter.
Use defer for scripts that need the DOM or depend on other deferred scripts, ensuring order is maintained.

<html>
<head>
  <title>Async vs Defer</title>
  <script async>
    console.log("Async script executed!");
  </script>
  <script defer>
    console.log("Defer script executed!");
  </script>
  <script>
    console.log("HTML parsing continues, then inline script runs.");
  </script>
</head>
<body>
  <h1>Async & Defer Demo</h1>
  <p>Check the console to see the execution order.</p>
</body>
</html>

Resource Hint: `preconnect`

Resource hints give the browser clues about resources it will need soon, allowing it to start fetching them earlier.

<link rel="preconnect"> tells the browser to establish a connection to another domain early. This includes DNS lookup, TCP handshake, and TLS negotiation, saving precious milliseconds for critical third-party resources.

Resource Hint: `preload`

<link rel="preload"> tells the browser to fetch a resource that is critically important for the current navigation as soon as possible. This is useful for resources like fonts, critical CSS, or images that are discovered late by the parser.

<html>
<head>
  <title>Preload Example</title>
  <link rel="preload" href="data:text/css;base64,Ym9keSB7IGJhY2tncm91bmQtY29sb3I6IGxpZ2h0Ymx1ZTsgfQ==" as="style">
  <style>
    /* This is a simple inline style */
    body { margin: 20px; }
  </style>
  <style>
    /* The preloaded style will apply */
    @import url("data:text/css;base64,Ym9keSB7IGJhY2tncm91bmQtY29sb3I6IGxpZ2h0Ymx1ZTsgfQ==");
  </style>
</head>
<body>
  <h1>Preloaded Style</h1>
  <p>The CSS for the light blue background is preloaded, ensuring it's available early.</p>
</body>
</html>

Resource Hint: `prefetch`

<link rel="prefetch"> tells the browser to fetch a resource that might be needed for a future navigation. It's a lower priority hint than preload and is great for speeding up subsequent page loads.

For example, if you know a user is likely to click a specific link, you can prefetch the resources for that page.

Prioritization Quiz

Which of the following statements about script loading and resource hints are TRUE?

Recap: Faster Page Loads

We've learned powerful techniques to prioritize content and speed up your web pages:

`defer` for non-blocking script loading, preserving execution order.
`async` for non-blocking, independent script execution.
`preconnect` to warm up connections to other domains.
`preload` to fetch critical resources early for the current page.
`prefetch` to fetch resources for future navigations.

By strategically using these, you can significantly improve your website's perceived performance and user experience!

자주 묻는 질문

“속도를 위한 콘텐츠 우선순위 지정” 강의는 무료인가요?

네 — “속도를 위한 콘텐츠 우선순위 지정” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 Web Performance Optimization & Lighthouse 강의 전체를 잠금 해제할 수 있습니다. Web Performance Optimization & Lighthouse 강의에는 총 4개의 강의가 포함되어 있습니다.

“속도를 위한 콘텐츠 우선순위 지정”에서 뭘 배우나요?

`async`, `defer`, 리소스 힌트와 같은 기법을 구현하여 중요한 콘텐츠의 우선순위를 정하고 체감 성능을 개선합니다. 브라우저에서 직접 실행하는 실습 코드로 Web Performance Optimization & Lighthouse을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

Web Performance Optimization & Lighthouse을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 Web Performance Optimization & Lighthouse은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 3번째 강의입니다.

“속도를 위한 콘텐츠 우선순위 지정” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 Web Performance Optimization & Lighthouse 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 Web Performance Optimization & Lighthouse 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

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