If element is in viewport- stop scroll animation

问题

Hi I followed a tutorial: http://css-tricks.com/slide-in-as-you-scroll-down-boxes/

It is working just fine, however, when an element is already in viewport (like if the browser is small and the page is loaded), then the jQuery doesn't add the CLASS to transition until AFTER scroll.

Is there a way to check if an element is already in viewport on load and then add a class of 'already-viewed?'

回答1:

Try

var viewed = Array.prototype.map.call(document.querySelectorAll("body *")
             , function (el, i) {
                return (el.getBoundingClientRect().bottom <= window.innerHeight 
                    && el.getBoundingClientRect().left <= window.innerWidth) 
                    && $(el).addClass("already-viewed") && el
             }).filter(Boolean);

$(document).ready(function () {
    var body = $("body");
    $.each(new Array(180), function () {
        body.append(
        $("<img>"))
    });
    
    var viewed = Array.prototype.map.call(document.querySelectorAll("body *"), function (el, i) {
        return (el.getBoundingClientRect().bottom <= window.innerHeight 
               && el.getBoundingClientRect().left <= window.innerWidth) 
               && $(el).addClass("already-viewed") && el
    }).filter(Boolean);
    body
    .append("total images: " + $("img").length 
                + ", already viewed: " + $(".already-viewed").length);
    console.log(viewed.length, $(viewed))
});

body {
    width : 1000px;
    height : 1000px;
}
img {
    width : 50px;
    height : 50px;
    background : navy;
}
.already-viewed {
    outline:0.15em solid red;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

来源：https://stackoverflow.com/questions/28397804/if-element-is-in-viewport-stop-scroll-animation