在windows上滚动，在最近的选择器上添加类

Question

我正试图在图像显示时添加类。JSFIDDLE

我有两张照片。当任何图像出现在屏幕上时，我正在尝试添加类。现在只添加第一张图片。我试图通过closest((进行检查，但没有得到任何值

function isScrolledIntoView(elem) {
var docViewTop = $(window).scrollTop();
var docViewBottom = docViewTop + $(window).height();
var elemTop = $(elem).offset().top;
return ((elemTop <= docViewBottom) && (elemTop >= docViewTop));
}
$(window).scroll(function(){

if (isScrolledIntoView('.box')) {
console.log($(this).find('img').html()); 
$('img').addClass('animated flip').css('background', 'red');
//added background red so you can see it has triggered
}
else {
$('img').removeClass('animated flip');
}

});

.col-md-12 {
height: 1500px;
padding-top: 1000px;
}
.box{
position:relative;
}
.animated {
opacity: 1;
visibility: visible;
transition: opacity 1s 0s, visibility 1s 0s;
z-index: 2;
position: fixed;
top: 0;
left: 0;
}
.rad-slideshow-item {
/* position: relative; */
}
.rad-slideshow-item .rad-asset-wrapper {

display: block;
padding: 0;
position: absolute;
top: 0;
left: 0;
overflow: hidden;
z-index: 3;
}
.animated .rad-slideshow-item.active-adjacent div.rad-asset-wrapper {
background: #000;
opacity: 0;
visibility: hidden;
position: fixed;
top: 0;
left: 0;
transition: opacity 0s 0s, visibility 0s 0s;
z-index: 1;
display: none;
}
.animated .rad-slideshow-item.active-adjacent div.rad-asset-wrapper {
display: block;
transform: translate3d(0, 0, 0);
transition: opacity 0s 1s, visibility 0s 1s;
}
.rad-spinner {
position: absolute;
top: 50%;
left: 50%;
z-index: 2;
transform: translate3d(-50%, -50%, 0);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<div class="col-md-12 ">
<div class="box">
<img src="https://dummyimage.com/800x800" class="icon"/>
<div class="rad-slideshow-item active-adjacent">

<div class="rad-asset-wrapper">
<h1>WEB<br/>DESIGN</h1>
</div>
</div>

</div>
<div class="box">
<img src="https://dummyimage.com/800x800" class="icon"/>
<div class="rad-slideshow-item active-adjacent">

<div class="rad-asset-wrapper">
<h1>WEB<br/>DESIGN</h1>
</div>
</div>

</div>

</div>

Answer 1

用于检查元素是否存在于视口中的函数。elementInViewport取自该SO_ Answer。多了解一下。

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 + window.innerHeight) &&
left < (window.pageXOffset + window.innerWidth) &&
(top + height) > window.pageYOffset &&
(left + width) > window.pageXOffset
);
}

jsFiddle演示了如果视口中存在console.log元素状态。

Answer 2

您可以使用ScrollMonitor

var el = $(".box");
var watcher = scrollMonitor.create( el );
watcher.enterViewport(function() {
console.log( 'I have entered the viewport' );
el.addClass('animated flip').css('background', 'red');
});
watcher.exitViewport(function() {
console.log( 'I have left the viewport' );
el.removeClass('animated flip').css('background', 'none');
});

http://jsfiddle.net/6p2hwe8x/2/