megurock/parallax.html

## parallax.html
<!DOCTYPE html>
<html lang="ja">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body {
        margin: 0;
      }
      .foo {
        background-color: yellow;
        height: calc(100vh + 100px);
      }
      .bar {
        background-color: orange;
        height: 2000px;
      }
      .parallax {
        position: relative;
      }
      /* これは IntersectionObserver の監視ターゲットとして機能します。 */
      .parallax__detector {
        position: absolute;
        top: 0;
        left: 0;
        width: 100px;
        height: 50vh;
        background-color: rgba(255, 0, 0, 0.5);
        pointer-events: none;
      }
      .parallax__image {
        aspect-ratio: 16/4;
        object-fit: cover;
        width: 100%;
        height: auto;
        display: block;
      }
    </style>
  </head>
  <body>
    <div class="foo"></div>
    <div class="parallax">
      <div class="parallax__detector"></div>
      <img
        class="parallax__image"
        src="https://via.placeholder.com/1600x1200"
      />
    </div>
    <div class="bar"></div>
  </body>
  <script>
    const onInterSect = ([entry], observer) => {
      console.log("ratio", entry.intersectionRatio);
    };

    const init = () => {
      const observerOptions = {
        rootMargin: "0px 0px -100px 0px",
        threshold: Array.from({ length: 101 }, (_, i) => i * 0.01), // 0 から 1 を要素とする配列
      };
      const observer = new IntersectionObserver(onInterSect, observerOptions);
      observer.observe(document.querySelector(".parallax__detector"));
    };

    init();
  </script>
</html>
	<!DOCTYPE html>
	<html lang="ja">
	<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<title>Document</title>
	<style>
	body {
	margin: 0;
	}
	.foo {
	background-color: yellow;
	height: calc(100vh + 100px);
	}
	.bar {
	background-color: orange;
	height: 2000px;
	}
	.parallax {
	position: relative;
	}
	/* これは IntersectionObserver の監視ターゲットとして機能します。 */
	.parallax__detector {
	position: absolute;
	top: 0;
	left: 0;
	width: 100px;
	height: 50vh;
	background-color: rgba(255, 0, 0, 0.5);
	pointer-events: none;
	}
	.parallax__image {
	aspect-ratio: 16/4;
	object-fit: cover;
	width: 100%;
	height: auto;
	display: block;
	}
	</style>
	</head>
	<body>
	<div class="foo"></div>
	<div class="parallax">
	<div class="parallax__detector"></div>
	<img
	class="parallax__image"
	src="https://via.placeholder.com/1600x1200"
	/>
	</div>
	<div class="bar"></div>
	</body>
	<script>
	const onInterSect = ([entry], observer) => {
	console.log("ratio", entry.intersectionRatio);
	};

	const init = () => {
	const observerOptions = {
	rootMargin: "0px 0px -100px 0px",
	threshold: Array.from({ length: 101 }, (_, i) => i * 0.01), // 0 から 1 を要素とする配列
	};
	const observer = new IntersectionObserver(onInterSect, observerOptions);
	observer.observe(document.querySelector(".parallax__detector"));
	};

	init();
	</script>
	</html>