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
在我看来,非常简单:
function isVisible(elem) {
var coords = elem.getBoundingClientRect();
return Math.abs(coords.top) <= coords.height;
}
其他回答
我发现这里公认的答案对于大多数用例来说过于复杂。这段代码很好地完成了工作(使用jQuery),并区分了完全可见和部分可见的元素:
var element = $("#element");
var topOfElement = element.offset().top;
var bottomOfElement = element.offset().top + element.outerHeight(true);
var $window = $(window);
$window.bind('scroll', function() {
var scrollTopPosition = $window.scrollTop()+$window.height();
var windowScrollTop = $window.scrollTop()
if (windowScrollTop > topOfElement && windowScrollTop < bottomOfElement) {
// Element is partially visible (above viewable area)
console.log("Element is partially visible (above viewable area)");
} else if (windowScrollTop > bottomOfElement && windowScrollTop > topOfElement) {
// Element is hidden (above viewable area)
console.log("Element is hidden (above viewable area)");
} else if (scrollTopPosition < topOfElement && scrollTopPosition < bottomOfElement) {
// Element is hidden (below viewable area)
console.log("Element is hidden (below viewable area)");
} else if (scrollTopPosition < bottomOfElement && scrollTopPosition > topOfElement) {
// Element is partially visible (below viewable area)
console.log("Element is partially visible (below viewable area)");
} else {
// Element is completely visible
console.log("Element is completely visible");
}
});
下面是一个函数,它告诉你一个元素在父元素的当前视口中是否可见:
function inParentViewport(el, pa) {
if (typeof jQuery === "function"){
if (el instanceof jQuery)
el = el[0];
if (pa instanceof jQuery)
pa = pa[0];
}
var e = el.getBoundingClientRect();
var p = pa.getBoundingClientRect();
return (
e.bottom >= p.top &&
e.right >= p.left &&
e.top <= p.bottom &&
e.left <= p.right
);
}
在我看来,非常简单:
function isVisible(elem) {
var coords = elem.getBoundingClientRect();
return Math.abs(coords.top) <= coords.height;
}
对于类似的挑战,我非常喜欢这个要点,它为scrollIntoViewIfNeeded()暴露了一个填充。
所有必要的功夫都需要回答这个问题:
var parent = this.parentNode,
parentComputedStyle = window.getComputedStyle(parent, null),
parentBorderTopWidth = parseInt(parentComputedStyle.getPropertyValue('border-top-width')),
parentBorderLeftWidth = parseInt(parentComputedStyle.getPropertyValue('border-left-width')),
overTop = this.offsetTop - parent.offsetTop < parent.scrollTop,
overBottom = (this.offsetTop - parent.offsetTop + this.clientHeight - parentBorderTopWidth) > (parent.scrollTop + parent.clientHeight),
overLeft = this.offsetLeft - parent.offsetLeft < parent.scrollLeft,
overRight = (this.offsetLeft - parent.offsetLeft + this.clientWidth - parentBorderLeftWidth) > (parent.scrollLeft + parent.clientWidth),
alignWithTop = overTop && !overBottom;
这指的是你想知道的元素,例如,overTop或overBottom -你只需要得到漂移…
这是我的解决方案。如果一个元素隐藏在一个可滚动的容器中,它将工作。
这里是一个演示(尝试调整窗口大小为)
var visibleY = function(el){
var top = el.getBoundingClientRect().top, rect, el = el.parentNode;
do {
rect = el.getBoundingClientRect();
if (top <= rect.bottom === false)
return false;
el = el.parentNode;
} while (el != document.body);
// Check it's within the document viewport
return top <= document.documentElement.clientHeight;
};
我只需要检查它在Y轴上是否可见(用于滚动Ajax加载更多记录功能)。