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JS-运动基础——案例应用：淡入淡出效果

<!DOCTYPE html>
<html>

    <head>
        <meta charset="UTF-8">
        <title>淡入淡出</title>
        <style type="text/css">
            .div {
                width: 100px;
                height: 100px;
                background-color: red;
                margin-top: 50px;
                position: absolute;
                left: 100px;
                top: 0;
                cursor: pointer;
                opacity: 0.3;
                filter: alpha(opacity:30);
            }
        </style>
        <script type="text/javascript">
        window.onload = function(){
            var oDiv = document.getElementById('div');
            oDiv.onmouseover = function(){
                start(100);
            };
            oDiv.onmouseout = function(){
                start(30);
            }
        }
            var alpha = 30;//关键点
            var timer =null;
        function start(iTarget){
            var oDiv = document.getElementById('div');
            clearInterval(timer);
            timer = setInterval(function (){
            var speed = 0;
            if(alpha < iTarget){
                speed = 10;
            }else{
                speed = -10;
            };
            if(alpha == iTarget){
                clearInterval(timer)
            }else{
                alpha+=speed;//关键点——忘了这一句。
                oDiv.style.filter = 'alpha(opacity:'+alpha+')';
                oDiv.style.opacity = alpha/100;
            }
        },30);
        }
        
        </script>
    </head>

    <body>
        <div class="div" id="div"></div>
    </body>

</html>

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原文地址：https://www.cnblogs.com/padding1015/p/6403124.html