滚动后到达视口时如何自动将焦点设置在 <input> 字段上？

Question

我知道 autofocus 属性：

<input type="email" id="hello" placeholder="a@b.com" autofocus>

自动将焦点设置在 HTML 输入上。

但是当页面远高于浏览器高度时，有没有办法（有一个特殊值autofocus？）只有当滚动后<input> 到达视口/页面当前可见部分？

Answer 1

function handleScroll() {
    var el = document.getElementById('hello')
    var rect = el.getBoundingClientRect();
    var elemTop = rect.top;
    var elemBottom = rect.bottom;

    // Only completely visible elements return true:
    var isVisible = (elemTop >= 0) && (elemBottom <= window.innerHeight);
    // Partially visible elements return true:
    //isVisible = elemTop < window.innerHeight && elemBottom >= 0;
    if (isVisible) el.focus();
}

<body onscroll="handleScroll()" style="overflow: scroll;">
  <input id="hello" type="email" placeholder="a@b.com" style="margin-top: 500px; margin-bottom: 200px;" />
</body>

滚动后到达视口时如何自动将焦点设置在 <input> 字段上？

How to automatically set focus on a <input> field when it arrives in the viewport after scrolling?

javascript

html

browser

viewport

html-input