是否有一种有效的方法来判断DOM元素(在HTML文档中)当前是否可见(出现在视口中)?
(这个问题指的是Firefox。)
是否有一种有效的方法来判断DOM元素(在HTML文档中)当前是否可见(出现在视口中)?
(这个问题指的是Firefox。)
当前回答
这里所有的答案都是确定元素是否完全包含在视口中,而不仅仅是以某种方式可见。例如,如果在视图的底部只有图像的一半可见,这里的解决方案将失败,考虑到“外部”。
我有一个用例,我正在通过IntersectionObserver进行惰性加载,但由于弹出过程中发生的动画,我不想观察任何已经在页面加载上交叉的图像。为此,我使用了以下代码:
const bounding = el.getBoundingClientRect();
const isVisible = (0 < bounding.top && bounding.top < (window.innerHeight || document.documentElement.clientHeight)) ||
(0 < bounding.bottom && bounding.bottom < (window.innerHeight || document.documentElement.clientHeight));
这基本上是检查顶部或底部边界是否在视口中独立。另一端可能在外面,但只要一端在里面,它至少是部分“可见”的。
其他回答
更新:时间在流逝,我们的浏览器也是如此。这种方法不再被推荐,如果你不需要支持ie7之前的版本,你应该使用Dan的解决方案。
原来的解决方案(现已过时):
这将检查元素是否在当前视口中完全可见:
function elementInViewport(el) {
var top = el.offsetTop;
var left = el.offsetLeft;
var width = el.offsetWidth;
var height = el.offsetHeight;
while(el.offsetParent) {
el = el.offsetParent;
top += el.offsetTop;
left += el.offsetLeft;
}
return (
top >= window.pageYOffset &&
left >= window.pageXOffset &&
(top + height) <= (window.pageYOffset + window.innerHeight) &&
(left + width) <= (window.pageXOffset + window.innerWidth)
);
}
你可以简单地修改它,以确定元素的任何部分在视口中是否可见:
function elementInViewport2(el) {
var top = el.offsetTop;
var left = el.offsetLeft;
var width = el.offsetWidth;
var height = el.offsetHeight;
while(el.offsetParent) {
el = el.offsetParent;
top += el.offsetTop;
left += el.offsetLeft;
}
return (
top < (window.pageYOffset + window.innerHeight) &&
left < (window.pageXOffset + window.innerWidth) &&
(top + height) > window.pageYOffset &&
(left + width) > window.pageXOffset
);
}
我尝试了Dan的答案,然而,用于确定边界的代数意味着元素必须既≤视口大小,又完全在视口内才能为真,很容易导致假否定。如果你想确定一个元素是否在视口中,ryanve的答案是接近的,但被测试的元素应该与视口重叠,所以试试这个:
function isElementInViewport(el) {
var rect = el.getBoundingClientRect();
return rect.bottom > 0 &&
rect.right > 0 &&
rect.left < (window.innerWidth || document.documentElement.clientWidth) /* or $(window).width() */ &&
rect.top < (window.innerHeight || document.documentElement.clientHeight) /* or $(window).height() */;
}
/**
* Returns Element placement information in Viewport
* @link https://stackoverflow.com/a/70476497/2453148
*
* @typedef {object} ViewportInfo - Whether the element is…
* @property {boolean} isInViewport - fully or partially in the viewport
* @property {boolean} isPartiallyInViewport - partially in the viewport
* @property {boolean} isInsideViewport - fully inside viewport
* @property {boolean} isAroundViewport - completely covers the viewport
* @property {boolean} isOnEdge - intersects the edge of viewport
* @property {boolean} isOnTopEdge - intersects the top edge
* @property {boolean} isOnRightEdge - intersects the right edge
* @property {boolean} isOnBottomEdge - is intersects the bottom edge
* @property {boolean} isOnLeftEdge - is intersects the left edge
*
* @param el Element
* @return {Object} ViewportInfo
*/
function getElementViewportInfo(el) {
let result = {};
let rect = el.getBoundingClientRect();
let windowHeight = window.innerHeight || document.documentElement.clientHeight;
let windowWidth = window.innerWidth || document.documentElement.clientWidth;
let insideX = rect.left >= 0 && rect.left + rect.width <= windowWidth;
let insideY = rect.top >= 0 && rect.top + rect.height <= windowHeight;
result.isInsideViewport = insideX && insideY;
let aroundX = rect.left < 0 && rect.left + rect.width > windowWidth;
let aroundY = rect.top < 0 && rect.top + rect.height > windowHeight;
result.isAroundViewport = aroundX && aroundY;
let onTop = rect.top < 0 && rect.top + rect.height > 0;
let onRight = rect.left < windowWidth && rect.left + rect.width > windowWidth;
let onLeft = rect.left < 0 && rect.left + rect.width > 0;
let onBottom = rect.top < windowHeight && rect.top + rect.height > windowHeight;
let onY = insideY || aroundY || onTop || onBottom;
let onX = insideX || aroundX || onLeft || onRight;
result.isOnTopEdge = onTop && onX;
result.isOnRightEdge = onRight && onY;
result.isOnBottomEdge = onBottom && onX;
result.isOnLeftEdge = onLeft && onY;
result.isOnEdge = result.isOnLeftEdge || result.isOnRightEdge ||
result.isOnTopEdge || result.isOnBottomEdge;
let isInX =
insideX || aroundX || result.isOnLeftEdge || result.isOnRightEdge;
let isInY =
insideY || aroundY || result.isOnTopEdge || result.isOnBottomEdge;
result.isInViewport = isInX && isInY;
result.isPartiallyInViewport =
result.isInViewport && result.isOnEdge;
return result;
}
这检查元素是否至少部分在视图中(垂直维度):
function inView(element) {
var box = element.getBoundingClientRect();
return inViewBox(box);
}
function inViewBox(box) {
return ((box.bottom < 0) || (box.top > getWindowSize().h)) ? false : true;
}
function getWindowSize() {
return { w: document.body.offsetWidth || document.documentElement.offsetWidth || window.innerWidth, h: document.body.offsetHeight || document.documentElement.offsetHeight || window.innerHeight}
}
查看verge的源代码,它使用getBoundingClientRect。这就像:
function inViewport (element) {
if (!element) return false;
if (1 !== element.nodeType) return false;
var html = document.documentElement;
var rect = element.getBoundingClientRect();
return !!rect &&
rect.bottom >= 0 &&
rect.right >= 0 &&
rect.left <= html.clientWidth &&
rect.top <= html.clientHeight;
}
如果元素的任何部分在视口中,则返回true。