我通过AJAX加载元素。其中一些只有当你向下滚动页面时才能看到。有什么方法可以知道元素现在是否在页面的可见部分?
当前回答
我改编了这个简短的jQuery函数扩展,你可以自由使用(MIT许可)。
/**
* returns true if an element is visible, with decent performance
* @param [scope] scope of the render-window instance; default: window
* @returns {boolean}
*/
jQuery.fn.isOnScreen = function(scope){
var element = this;
if(!element){
return;
}
var target = $(element);
if(target.is(':visible') == false){
return false;
}
scope = $(scope || window);
var top = scope.scrollTop();
var bot = top + scope.height();
var elTop = target.offset().top;
var elBot = elTop + target.height();
return ((elBot <= bot) && (elTop >= top));
};
其他回答
我只是想分享一下,我把这个和我的脚本结合起来移动div,这样它就总是在视图中:
$("#accordion").on('click', '.subLink', function(){
var url = $(this).attr('src');
updateFrame(url);
scrollIntoView();
});
$(window).scroll(function(){
changePos();
});
function scrollIntoView()
{
var docViewTop = $(window).scrollTop();
var docViewBottom = docViewTop + $(window).height();
var elemTop = $("#divPos").offset().top;
var elemBottom = elemTop + $("#divPos").height();
if (elemTop < docViewTop){
$("#divPos").offset({top:docViewTop});
}
}
function changePos(){
var scrTop = $(window).scrollTop();
var frmHeight = $("#divPos").height()
if ((scrTop < 200) || (frmHeight > 800)){
$("#divPos").attr("style","position:absolute;");
}else{
$("#divPos").attr("style","position:fixed;top:5px;");
}
}
我需要检查可滚动DIV容器内元素的可见性
//p = DIV container scrollable
//e = element
function visible_in_container(p, e) {
var z = p.getBoundingClientRect();
var r = e.getBoundingClientRect();
// Check style visiblilty and off-limits
return e.style.opacity > 0 && e.style.display !== 'none' &&
e.style.visibility !== 'hidden' &&
!(r.top > z.bottom || r.bottom < z.top ||
r.left > z.right || r.right < z.left);
}
function isScrolledIntoView(elem) {
var docViewTop = $(window).scrollTop(),
docViewBottom = docViewTop + $(window).height(),
elemTop = $(elem).offset().top,
elemBottom = elemTop + $(elem).height();
//Is more than half of the element visible
return ((elemTop + ((elemBottom - elemTop)/2)) >= docViewTop && ((elemTop + ((elemBottom - elemTop)/2)) <= docViewBottom));
}
使用IntersectionObserver API
(在现代浏览器中本机)
通过使用观察器来确定一个元素在视口中是否可见,或者在任何可滚动的容器中是否可见,这是非常简单有效的。
无需附加滚动事件并手动检查事件回调,这更有效:
//定义一个观察者实例 var观察者= new IntersectionObserver(onIntersection, { Root: null, // default为视口 阈值:目标可见区域的。5 //百分比。触发“onIntersection” }) //在交集变化时调用回调函数 函数onIntersection(条目,opts){ 条目。forEach(入口= > entry.target.classList。切换(“可见”,entry.isIntersecting) ) } //使用观察者来观察一个元素 观察者。观察(document.querySelector('.box')) //停止观察: / / observer.unobserve (entry.target) 跨度{:固定;上图:0;左:0;} .box{宽度:100 px;身高:100 px;背景:红色;保证金:1000 px;过渡:综合成绩;} .box。可见{背景:绿色;这个特性:50%;} <span>纵向滚动&水平…< / span > < div class = '盒子' > < / div >
现代浏览器(包括移动浏览器)支持。IE - View浏览器支持表中不支持
这里有另一个解决方案:
<script type="text/javascript">
$.fn.is_on_screen = function(){
var win = $(window);
var viewport = {
top : win.scrollTop(),
left : win.scrollLeft()
};
viewport.right = viewport.left + win.width();
viewport.bottom = viewport.top + win.height();
var bounds = this.offset();
bounds.right = bounds.left + this.outerWidth();
bounds.bottom = bounds.top + this.outerHeight();
return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
};
if( $('.target').length > 0 ) { // if target element exists in DOM
if( $('.target').is_on_screen() ) { // if target element is visible on screen after DOM loaded
$('.log').html('<div class="alert alert-success">target element is visible on screen</div>'); // log info
} else {
$('.log').html('<div class="alert">target element is not visible on screen</div>'); // log info
}
}
$(window).on('scroll', function(){ // bind window scroll event
if( $('.target').length > 0 ) { // if target element exists in DOM
if( $('.target').is_on_screen() ) { // if target element is visible on screen after DOM loaded
$('.log').html('<div class="alert alert-success">target element is visible on screen</div>'); // log info
} else {
$('.log').html('<div class="alert">target element is not visible on screen</div>'); // log info
}
}
});
</script>
在JSFiddle中可以看到