Lazy Load

程式碼

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Sora", system-ui, sans-serif;
  background: #080d18;
  color: #e2e8f0;
}

.shell {
  width: min(960px, calc(100% - 2rem));
  margin: 2rem auto;
}

p {
  color: #94a3b8;
}

.gallery {
  display: grid;
  gap: 1rem;
}

figure {
  margin: 0;
  min-height: 280px;
  border-radius: 16px;
  overflow: hidden;
  border: 1px solid rgba(255, 255, 255, 0.14);
  background: linear-gradient(120deg, #1d2638, #101828);
  position: relative;
}

figure::after {
  content: "Loading";
  position: absolute;
  right: 0.8rem;
  top: 0.8rem;
  font-size: 0.75rem;
  color: #cbd5e1;
  background: rgba(15, 23, 42, 0.72);
  border-radius: 999px;
  padding: 0.15rem 0.45rem;
}

figure.loaded::after {
  display: none;
}

img {
  width: 100%;
  height: auto;
  display: block;
  opacity: 0;
  filter: blur(16px);
  transform: scale(1.03);
  transition: opacity 0.35s ease, filter 0.35s ease, transform 0.35s ease;
}

img.loaded {
  opacity: 1;
  filter: blur(0);
  transform: scale(1);
}

(() => {
  const images = Array.from(document.querySelectorAll("img[data-src]"));

  const loadImage = (img) => {
    const src = img.getAttribute("data-src");
    if (!src) return;

    img.src = src;
    img.addEventListener(
      "load",
      () => {
        img.classList.add("loaded");
        img.parentElement?.classList.add("loaded");
      },
      { once: true }
    );
    img.removeAttribute("data-src");
  };

  if (!("IntersectionObserver" in window)) {
    images.forEach(loadImage);
    return;
  }

  const observer = new IntersectionObserver(
    (entries) => {
      for (const entry of entries) {
        if (!entry.isIntersecting) continue;
        const img = entry.target;
        if (img instanceof HTMLImageElement) {
          loadImage(img);
          observer.unobserve(img);
        }
      }
    },
    { rootMargin: "120px" }
  );

  for (const img of images) {
    observer.observe(img);
  }
})();

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Lazy Load</title>
  <link rel="stylesheet" href="style.css" />
</head>
<body>
  <main class="shell">
    <h1>Lazy Load Images</h1>
    <p>Images load only when entering the viewport.</p>

    <section class="gallery" id="gallery">
      <figure>
        <img data-src="https://picsum.photos/seed/phase14-a/900/520" alt="Landscape 1" width="900" height="520" />
      </figure>
      <figure>
        <img data-src="https://picsum.photos/seed/phase14-b/900/520" alt="Landscape 2" width="900" height="520" />
      </figure>
      <figure>
        <img data-src="https://picsum.photos/seed/phase14-c/900/520" alt="Landscape 3" width="900" height="520" />
      </figure>
      <figure>
        <img data-src="https://picsum.photos/seed/phase14-d/900/520" alt="Landscape 4" width="900" height="520" />
      </figure>
      <figure>
        <img data-src="https://picsum.photos/seed/phase14-e/900/520" alt="Landscape 5" width="900" height="520" />
      </figure>
    </section>
  </main>

  <script src="script.js"></script>
</body>
</html>

A practical media performance pattern for content-heavy pages.

Features

Deferred image loading
Blur placeholder state
Fade-in reveal when loaded
Fallback for non-supporting environments