【js】元素是否在可视区范围内
公式:元素到顶部距离(最近的具有定位父级元素)- 滚动条高度 <= 可视区的高度
offsetTop、scrollTop
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <style> .div { height: 2000px; } p { height: 200px; background: red; } </style> </head> <body> <div class="div"></div> <p id="p">我出现啦</p> <!-- 通过元素位置关系方法--> <script> function isContain(dom) { // 获取可视窗口的盖度。 const screenHeight = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight; // 获取滚动条滚动的高度 const scrollTop = document.documentElement.scrollTop; // 获取元素偏移的高度。就是距离可视窗口的偏移量。 const offsetTop = dom.offsetTop; return offsetTop - scrollTop <= screenHeight; } const p = document.getElementById("p"); window.onscroll = () => { if (isContain(p)) { document.body.style.backgroundColor = 'blue' } else { document.body.style.backgroundColor = 'green' } } </script> <!-- 通过 getBoundingClientRect方法--> <!-- <script> // 只有当子元素全部出现在父元素中时,才会返回true。 function isContain(dom) { const totalHeight = window.innerHeight || document.documentElement.clientHeight; const totalWidth = window.innerWidth || document.documentElement.clientWidth; // 当滚动条滚动时,top, left, bottom, right时刻会发生改变。 const { top, right, bottom, left } = dom.getBoundingClientRect(); console.log(top, right, bottom, left) return (top >= 0 && left >= 0 && right <= totalWidth && bottom <= totalHeight); } const p = document.getElementById("p"); window.onscroll = () => { if (isContain(p)) { document.body.style.backgroundColor = 'blue' } else { document.body.style.backgroundColor = 'green' } } </script> --> <!-- 通过new IntersectionObserver(); --> <!-- <script> const observer = new IntersectionObserver((entries) => { if (entries[0].isIntersecting) { document.body.style.backgroundColor = "blue" } else { document.body.style.backgroundColor = "green" } }, { threshold: .2 }); const p = document.getElementById("p") observer.observe(p) </script> --> </body> </html>
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